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Using Rewriting-Logic Notation for Funcional Verification in Data-Stream Based Reconfigurable ComputingReiner W. Hartenstein1, Ricardo P. Jacobi2 1Fachbereich Informatik Kaiserslautern University of Technology hartenst@rhhk.uni-kl.de2Depto. De Ciência da ComputaçãoUniversidade de Brasíliarjacobi@cic.unb.br Maurício Ayala-Rincón3, Carlos H. Llanos4 3Departamento de Matemáticaayala@mat.unb.br4Departamento de Engenharia Mecânicallanos@unb.brUniversidade de BrasíliaBrasília - BrazilAbstractReconfigurable Systolic Arrays are a generalization of Systolic Arrays where node operations and interconnections can be redefined even at run time. This flexibility increases the range of systolic array’s application, making the choice of the best systolic architecture to a given problem a critical task. In this work we investigate the specification and verification of such architectures using rewriting-logic, which provides a high level design framework for architectural exploration. In particular, we show how to use ELAN rewriting system to specify reconfigurable systems which can perform both arithmetic and symbolic computations.1. IntroductionThe widespread popularization of mobile computing and wireless communication systems fostered the research on new architectures to efficiently deal with communications issues in hardware constrained platforms like PDAs, mobile phones and pagers, for instance. Some tasks such as data compression, encoding and decoding are better implemented through dedicated hardware modules than using standard general purpose processors (GPP). However, the exploding costs of integrated circuit fabrics associated with shorter devices lifetimes makes the design of ASIC (Application Specific Integrated Circuit) a very expensive alternative. The growing capacity of Field Programmable Gate Arrays (FPGA) and the possibility of reconfiguring them to implement different hardware architectures makes it a good solution to this rapid changing wireless market. An FPGA may be configured to implement a cipher algorithm at one moment and can be later reconfigured to implement a data compressing algorithm. This flexibility opens a wide range of architectural alternatives to implement algorithms directly in hardware. In this context, it is very important to provide methods and tools to rapidly model and evaluate different hardware architectures to implement a given algorithm.In this paper we propose the use of rewriting systems to model and evaluate reconfigurable systolic hardware architectures. After the seminal work of Knuth-Bendix about the completion of algebraic equational specifications, which allows for the automatic generation of a rewrite-based theorem prover for the equational reduct of the subjacent treated theories [KnBe70], rewriting has been successfully applied into different areas of research in computer science as an abstract formalism for assisting the simulation, verification and deduction of complex computational objects and processes. In particular, in the context of computer architectures, rewriting theory has been applied as a tool for reasoning about hardware design.To review only a reduced set of different approaches in this direction, we find of great interest the work of Kapur who has used his well-known Rewriting Rule Laboratory - RRL(the first successful prover assistant based on rewriting) for verifying arithmetic circuits [KaSu2000, Ka2000, KaSu1997] as well as Arvind’s group that treated the implementation of processors with simple architectures [ShAr98a,ShAr98b,ArSh99], the rewrite-based description and synthesis of simple logical digital circuits [HoAr99] and the description of cache protocols over memory systems [RuShAr99,ArStSh01]. Also contributions in this field have shown how rewriting theory can be applied for the specification of processors (as Arvind’s group does) as well as for the purely rewrite based simulation and analysis of the specified processors [ANJLH02]. To achieve this rewriting-logic has been applied, that extends the pure rewriting paradigm allowing for a logical control of the application of the rewriting rules bystrategies [Me00,CiKi99]. Important programming environments based on the rewriting-logic paradigm are ELAN [CiKi99,BKKM02], Maude [Me00,Cla02] and Cafe-OBJ [DiFu02]. The impact of rewriting-logic as a successful programming paradigm in computer science as well as of the applicability of the related programming environments is witnessed by [MOMe02]. All our implementations and experiments were done in ELAN, since we consider of great flexibility its easy manipulation of strategies. However, for effects of model checking Maude has been proved to be more adequate.Section 2 provides an introduction to basic concepts in rewriting theory and reconfigurable circuits. Section 3 presents the specification and simulation of reconfigurable systolic arrays. Section 4 discusses use of rewriting-logic for simulating reconfiguration and another approach for data driven systolic arrays and section 5 is the conclusion.2. BackgroundAn example of our typical target environments is mapping applications onto platforms like coarse-grained DPAs (DataPath Arrays) or rDPAs (reconfigurable DPAs). We assume, that such platforms are completely pre-debugged, so that only the related mapping source has to be verified. Using Term Rewriting Systems (s. section 2.1) in such an environment means to specify or verify designs from sources at abstraction levels being higher than that of languages like VHDL or Verilog. Such notations are much more compact and concise than with traditional hardware language source notations in EDA. An example is the input language of ELAN which is a parsable derivative of the math formula space.This paper uses systolic arrays as demo examples (section 2.2). Systolic arrays, however, are special cases of super-systolic platforms like DPAs or rDPAs [HaKrRe95], which are data-stream-based [Ha03] pipe networks. (By the way: such platforms may also be emulated on larger FPGAs.) The only difference between systolic and super-systolic is the mapping method [Ha97]. Algebraic mapping or linear projection methods yield only solutions with linear uniform pipes which is restricted to the special case of applications with strictly regular data dependencies. But using simulated annealing, genetic algorithms or other optimization methods, permits any heterogeneous networks with free form pipes like zigzag, circular, or any much more wild shapes, and may also include forks and joins. The methodology introduced by this paper may be used for all kinds of data-stream-based hardwired or reconfigurable platforms.2.1. Rewriting theoryWe include the minimal needed notions on rewriting theory and rewriting-logic. For a detailed presentation of rewriting see [BaNi98].A Term Rewriting System, TRS for short, is defined as a triple ·R, S, S0 Ò, where S and R are respectively sets of terms and of rewrite rules of the form l ’ r i f p(l)being l and r terms and p a predicate and where S0 is the subset of initial terms of S. l and r are called the left-hand and right-hand sides of the rule and p its condition.In the architectural context of [ShAr98b], terms and rules represent states and state transitions, respectively.A term s can be rewritten or reduced to the term t, denoted by s ’ t, whenever there exists a subterm s' of s that can be transformed according to some rewrite rule into the term s'' such that replacing the occurrence of s' in s with s'' gives t. A term that cannot be rewritten is said to be in normal or canonical form. The relation over S given by the previous rewrite mechanism is called the rewrite relation of R and is denoted by ’. Its inverse is denoted by ¨and its reflexive-transitive closure by ’*and its equivalence closure by ´*.The important notions of terminating property (or Noetherianity) and Church-Rosser property or confluence are defined as usual. These notions correspond to the practical computational aspects as the determinism of processes and their finiteness.•a TRS is said to be terminating if there are no infinite sequences of the form s0’ s1’ ...• a TRS is said to be confluent if for all divergence of the form s ’* t 1, s ’* t 2 there exists a term u such that t 1 ’* u and t 2 ’* u .The use of the subset of initial terms S 0, representing possible initial states in the architectural context (which is not standard in rewriting theory), is simply to define what is a "legal" state according to the set of rewrite rules R ; i.e., t is a legal term (or state) whenever there exists an initial state s Œ S 0 such that s ’* t .Using these notions of rewriting one can model the operational semantics of algebraic operators and functions. Although in the pure rewriting context rules are applied in a truly non deterministic manner in the practice it is necessary to have a control of the ordering in which rules are applied. Thus rewriting theory jointly with logic, that is known as rewriting-logic, has been showed of practical applicability in this context of specification of processors since they may be adapted for representing in the necessary detail many hardware elements involved in processors. Moreover, other important fields of hardware design such as verification and synthesis of logical circuits may be benefited from the simplicity and versatility of this theoretical framework.2.2. Systolic arrays and reconfigurable systemsA systolic array is a mesh-connected pipe network of DPUs (datapath units), using only nearest neighbor (NN) interconnect [Ku78, Ku87]. DPU functional units operate synchronously, processing streams of data that traverse the network. Systolic arrays provide a large amount of parallelism and are well adapted to a restrict set of computational problems, i.e., those which can be efficiently mapped to a regular network of operators.Figure 1 shows a simple systolic example of a matrix-vector multiplication. The vector elements are stored inthe cells and are multiplied by the matrix elements thatare shifted bottom-up. On the first cycle, the first cell(DPU1) computes x 1*a 11, while the second and third cells(DPU2 and DPU3) multiply their values by 0. On thesecond cycle, the first cell computes x 1*a 21, while thesecond cell computes x 1*a 11 + x 2*a 12, where the first termis taken from the first cell and added to the productproduced in second cell. In the third cycle, the third cellproduces the first result : y 1 = x 1*a 11 + x 2*a 12 + x 3*a 13. Inthe following two cycles y 2 and y 3 will be output by thethird cell.There are several alternative configurations of functional cells, each one tailored to a particular class of computing problems. However, one of the main critics to systolic arrays is its restriction to applications with strictly regular data dependencies, as well as its lack of flexibility. Once designed, it is suitable to support only one particular application problem.The limitations of systolic arrays may be circumvented by using reconfigurable circuits, the most representative of them being the FPGAs (Field Programmable Gate Arrays). An FPGA can have its behavior redefined in such a way that it can implement completely different digital systems on the same chip. Fine grain FPGAs may redefine a circuit at the gate level, working with bit wide operators. This kind of architecture provides a lot of flexibility, but takes more time to reconfigure than coarse grain reconfigurable platforms (rDPAs: reconfigurable DPAs). These work with word wide operators that are slightly less flexible but more area efficient and take much less time to reconfigure than the fine grain ones. The design of reconfigurable systolic architectures [HaKrRe95, HHHN00] aims to overcome the restriction of pure systolic circuits while keeping the benefits of a large degree of parallelism. In the reconfigurable approach, the operations performed by each functional unit as well as the interconnection among them may be reconfigured in order to be adapted to different applications. Moreover, it is possible to change the configuration of the circuit during run time, an approach called dynamic reconfiguration, which broadens even more the architectural alternatives to implement applications in hardware.a 21a 31a 12a 22a 32a 13a 23a 330y 1 = a 11x 1+a 12x 2+a 13x 3y 2 = a 21x 1+a 22x 2+a 23x 3y 3 = a 31x 1+a 32x 2+a 33x 3Figure 1: Vector – matrix computation.3. Specification and Simulation of Systolic Arrays via Rewriting-LogicHere we show how rewriting-logic can be applied to specify simple systolic arrays for vector andmatrix multiplication using the ELAN system. In these systems we can consider as the reconfigurablepart the constants in each component (DPU as in Figure 1), here called MAC (Multiplier/Adder).Vector multiplication: ELAN provides a very flexible programming environment where the user defines the syntax and semantics of data types (called sorts) and operations to be used in the program.Figure 2 shows the syntax of the data types in the ELAN program that models the vector multiplication.In the left side of a definition the data is specified using a combination of text and place holders which are represented by an ‘@’ character. For instance, an element of sort Port is defined as port(@, @). Thesort of the parameters as well as the sort of the element itself is defined in the right side of the definition.In this example, the two parameters of port are an integer and a Boolean, and the resulting element port(int, bool) is of sort Port. A MAC data is composed of six elements. The sort of the elements is, respectively, int, for the identifier, two of sort Port and two of sort Reg for the ports and registers andone of sort Const for the respective constant component of the multiplier vector. The processor sort Procconsists of four components: three of sort MAC and one of sort DataStream. The DataStream isdescribed as an object with three components of sort list[Data].operators global@ : ( int ) Const;port(@,@): ( int bool ) Port;reg(@,@): ( int bool ) Reg;'[' @,@,@,@,@,@ ']': ( int Port Port Reg Reg Const ) MAC;'<' @ @ @ @ '>' : ( MAC MAC MAC DataStream ) Proc;( @ @ @ ): ( list[Data] list[Data] list[Data] ) DataStream;@: ( int ) Data;endFigure 2. Sorts of the MAC in ELANThe rule named sole, used to describe the behavior of the processor during each cycle of the execution is given in figure 4. Informally, the rule is fired when the expression being processed matches the left side of the rule. It is replaced by the expression produced at the right side of the rule, which is again matched against the set of rules that define the program. Rules can be named for future reference when defining strategies. The rule name sole appears between square brackets in the beginning of the rule. Observe that after one-step of reduction applying this rule all necessary changes in the specified processor are executed. First, notice that the data d1, d2 and d3 at the top of the DataStream, are removed from the three lists of data and placed in the first ports of the three MACs.Figure 3. MAC Systolic Array ArchitectureThe multiplications between the contents of each first port vpi1 and the corresponding constant c i are placed in the first register of each MAC, for i=1,2 3 and 3 and the additions between the first register vri1 and the second port vpi2 are placed in the second port of each MAC, for i=1,2 and 3. Zeros preceding each operator v i are included to synchronize the two operations executed in each MAC. Finally, observe the data transfer from the second register vri2 of each MAC to the second port of the next component vp(i+1)2for i=1 and 2. All that is simultaneously done by only one application of the rewriting rule sole.With respect to the timing aspects of this example, the model assumes a clocked operation like traditional systolic architectures. There is no handshake between nodes and each application of rule sole corresponds to a single clock cycle. Thus, each node in fig. 3 takes two clock cycles to produce itsoutput. The synchronization between nodes for the first values is achieved introducing pairs of zero values, as illustrated in figure 3, and the Boolean flags used to synchronize nodes could be omitted.Executing all steps with a singe rewriting rule could appear artificial in other contexts of computer science, such as semantics of programming languages and in general theory of computing. Nice but relatively complex theoretical results can be related with the possibility of having a unique rewriting rule which simulates a (universal) Turing machine [Da1989, Da1992]. This nontrivial theoretical development may be better understood when we relate a sole rule with the execution of a "cycle" of a processor.rules for Procd1,d2,d3 : int; // variables for input datal1,l2,l3 : list[Data]; // lists of input datavp11, vp12, vp21, vp22, vp31, vp32 : int; // portsvr11, vr12, vr21, vr22, vr31, vr32 : int; // registersc1, c2, c3 : int; // constantsglobal[sole]<[1,port(vp11,true),port(0,true),reg(vr11,true),reg(vr12,true),c1][2,port(vp21,true),port(vp22,true),reg(vr21,true),reg(vr22,true),c2][3,port(vp31,true),port(vp32,true),reg(vr31,true),reg(vr32,true),c3 ](d1.l1 d2.l2 d3.l3) > =><[1, port(d1,true),port(0,true),reg(vp11*c1,true), reg(0+vr11,true),c1 ][2, port(d2,true),port(vr12,true),reg(vp21*c2,true), reg(vp22+vr21,true),c2 ][3, port(d3,true),port(vr22,true),reg(vp31*c3,true), reg(vp32+vr31,true),c3 ](l1 l2 l3) >endendFigure 4. ELAN Description of the Sole Rule.For our example we will consider as simple mechanism of reconfiguration the possibility of changing the constants in each MAC. Then a computation with our systolic array consists of two stages: a reconfiguration stage, where the constants are set and the subsequent processor execution with the previously defined rule sole.Figure 5 shows one additional rule created for the reconfiguration of a processor called conf. It simply changes the contents of the constant part of each MAC(in our case by the vector (1,0,0)). Observe that with the pure rewriting based paradigm this rule applies infinitely, because the resulting expression will match against the left side of the rule again and again. Thus, for controlling its application, we define a logical strategy, called withconf.withconf simply allows for the execution of one-step of reduction with the rule conf(the first reconfiguration stage) and a subsequent normalization with the rule sole (the second processor execution stage). This normalization is an available ELAN strategy, which applies the rewriting rules given as argument (in our case the rule sole) until a normal form is reached.[conf]< [1,port(vp11,true),port(0,true),reg(vr11,true),reg(vr12,true),c1][2,port(vp21,true),port(vp22,true),reg(vr21,true),reg(vr22,true),c2][3,port(vp31,true),port(vp32,true),reg(vr31,true),reg(vr32,true),c3](d1.l1 d2.l2 d3.l3) > =>< [1,port(vp11,true),port(0,true),reg(vr11,true),reg(vr12,true),1][2,port(vp21,true),port(vp22,true),reg(vr21,true),reg(vr22,true),0][3,port(vp31,true),port(vp32,true),reg(vr31,true),reg(vr32,true),0](d1.l1 d2.l2 d3.l3) >endstrategies for Procimplicit[] withconf => conf; normalise(sole) end[] simple => normalise(sole) endendFigure 5. conf Rule for ReconfigurationMatrix Multiplication:figure 6 shows the matriz multiplication structure and the description of its components is given in figure 7. Using the previous approach (that is, specifying a sole rule) implies the use of an excessive number of variables, which is not directly supported in ELAN. In fact, we would need different variables for the two ports, three registers and the constant belonging to each MAC, whichgives a total of 96 variables; additionally, we would need 16 variables for describing the two 4x data streams. This could be done by enlarging the ELAN capacity for dealing with variables before compiling the system. But a better solution is to split the cycle defining independent rewriting rules to be applied under a reasonable strategy, to simulate the internal process into each MAC component and the propagation of data between each component to their North and East connected MAC s.We define a rule for each of the sixteen components, which propagates the contents into their registers two and three to their North and East connected components, respectively. As a consequence of the form in which data should be transferred in the processor, these sixteen rules should be applied from the right to the left and top-down in order to complete a whole cycle of execution.Figure 6. Systolic Matrix-vector multiplicationoperators global@ : ( int ) Const;p(@) : ( int ) Port;r(@) : ( int ) Reg;'['@,@,@,@,@,@,@']' : ( int Port Port Reg Reg Reg Const ) MAC;'<' @@ @ @ @@ @ @ @@ @ @ @@ @ @ @@ '>: ( DataStringMAC MAC MAC MAC // MACs 13 14 15 16MAC MAC MAC MAC // MACs 09 10 11 11MAC MAC MAC MAC // MACs 05 06 07 08MAC MAC MAC MAC // MACs 01 02 03 04DataString ) Proc;( @ @ @ @ ) : ( list[Data] list[Data] list[Data] list[Data] )DataString;@ : ( int ) Data;endFigure 7. A 4¥4 Systolic array DescriptionAll these rules are very similar and a selected group of them is presented in the Figure 8. The rules for the South (mac01, mac02, mac03, mac04) and West (mac01, mac05, mac09, mac13) MAC s, called boundary components of the processor, load the data (dS and dW) in the head of the corresponding list of the data stream (lS1, lS2, lS3, lS4 and lW1, lW2, lW3 and lW4). Moreover, the rules for MAC s in the North (mac13, mac14, mac15, mac16) and East (mac04, mac08, mac12, mac16) boundaries of the processor only transfer data to the East and North corresponding boundary components; except, of course, for mac16. Consequently, different orderings for applying these rules completing a whole cycle of the processor are possible. For instance, we could take the ordering: mac16, mac12, mac08, mac04, mac15, mac11, mac07, mac03, mac14, mac13, mac10, mac09, mac06, mac05, mac02, mac01.In the Figure 9 we present a possible strategy called onecycle which defines an(other) ordering of application of these rules for completing a sole cycle of the processor. For completing the simulation of execution with this simple processor, one should define a normalization via this strategy: normalise(onecycle). In this rewriting-logical environment, our specification could be easily modified allowing the interpretation of parts of the processors as reconfigurable components.At first glance, one could look at the constants of the 16 MAC s as a reconfigurable component. In this way the processor can be adapted to be either a 4-vector versus 4x4-matrix multiplier or vice-versa and the 4x4-matrix may be modified to represent, for example, either the identity or the matrix F 4 of the Fast Discrete Fourier Transform (FFT).rules for Proc m01,m02,m03,m04,m05,m06,m07,m08: MAC; // 1-8 MACs m09,m10,m11,m12,m13,m14,m15,m16:MAC; //9-16 MACs dW, dS : int; // data East and SouthlW1,lW2,lW3,lW4,lS1,lS2,lS3,lS4:list[Data]; // West andSouthr1,r2, r3,rN1,rN2,rN3 : int; // Central North andrE1,rE2,rE3 : int; // East registers 1,2,3p1,p2,pN1,pN2,pE1,pE2: int; //Central,North and East portsc,cE,cN : int;global[mac16]< (lW1 lW2 lW3 lW4)m13 m14 m15 [16,p(p1),p(p2),r(r1),r(r2),r(r3),c ]m09 m10 m11 m12m05 m06 m07 m08m01 m02 m03 m04(lS1 lS2 lS3 lS4) > =>< (lW1 lW2 lW3 lW4)m13 m14 m15 [16,p(p1),p(p2),r(p1*c),r(r1+p2),r(p1),c ]m09 m10 m11 m12m05 m06 m07 m08m01 m02 m03 m04(lS1 lS2 lS3 lS4) >end ...[mac11]< (lW1 lW2 lW3 lW4)m13 m14 [15,p(pN1),p(pN2),r(rN1),r(rN2),r(rN3),cN ] m16m09 m10 [11,p(p1),p(p2),r(r1),r(r2),r(r3),c ][12,p(pE1),p(pE2),r(rE1),r(rE2),r(rE3),cE ]m05 m06 m07 m08m01 m02 m03 m04(lS1 lS2 lS3 lS4) > =>< (lW1 lW2 lW3 lW4) m13 m14 [15,p(pN1),p(r2),r(rN1),r(rN2),r(rN3),cN ] m16 m09 m10 [11,p(p1),p(p2),r(p1*c),r(r1+p2),r(p1),c ] [12,p(r3),p(pE2),r(rE1),r(rE2),r(rE3),cE ] m05 m06 m07 m08 m01 m02 m03 m04 (lS1 lS2 lS3 lS4) >end ...…… [mac01]< (dW.lW1 lW2 lW3 lW4) m13 m14 m15 m16 m09 m10 m11 m12 [05,p(pN1),p(pN2),r(rN1),r(rN2),r(rN3),cN ] m06 m07 m08 [01,p(p1),p(p2),r(r1),r(r2),r(r3),c ] [02, p(pE1),p(pE2),r(rE1),r(rE2),r(rE3),cE]m03 m04 (dS.IS1) IS2 IS3 IS$) > =>< (IE1 IE2 IE3 IE4) m13 m14 m15 m16 m09 m10 m11 m12 [05, p(pN1),p(r2) r(rN1) r(rN2) r(rN3), cN] m06 m07 m08 [01, p(dW), p(dS),r(p1*c), r((rE2), r(rE3), cE] m03 m04 (IS1 IS2 IS3 IS4)>end end Figure 8. A selected set of rules for matrix-vector multiplipy.Strategies for Procimplicit[] onecycle =>mac16;mac15;mac14;mac13;mac12;mac11;mac10;mac09;mac08;mac07;mac06;mac05;mac04;mac03;mac02;mac01 end end Figure 9. onecycle strategy for rule application.reconfF4 => F4;normalise(mac16;mac15;mac14;mac13; mac12;mac11;mac10;mac09; mac08;mac07;mac06;mac05; mac04;mac03;mac02;mac01)endFigure 10: strategy working over processor.The last is specified by a strategy additional, that is presented at the Figure 11, which before to the simulation of the normalization executes the rewrite rule F 4. F 4 transforms any given state of the processor into another where the reconfigurable constants are replaced with the corresponding powers of a primitive complex 4-root of the unity of F 4 (either i o r -i ) as illustrated in the Figure 11. In this specification the components of each MAC have been divided into the fixed ones and the reconfigurable constant [fxnn cnn]. This simple idea can be directly extended to different kind of MAC s , where other components are considered to be reconfigurable.[F4]< dstreamEast[fx13 c13] [fx14 c14] [fx15 c15] [fx16 c16][fx09 c09] [fx10 c10] [fx11 c11] [fx12 c12][fx05 c05] [fx06 c06] [fx07 c07] [fx08 c08][fx01 c01] [fx02 c02] [fx03 c03] [fx04 c04]dstreamSouth > =>< dstreamEast [fx13 i 0] [fx14 i 3] [fx15 i 6] [fx16 i 9] [fx09 i 0] [fx10 i 2] [fx11 i 4] [fx12 i 6] [fx05 i 0] [fx06 i 1] [fx07 i 2] [fx08 i 3] [fx01 i 0] [fx02 i 0] [fx03 i 0] [fx04 i 0]dstreamSouth >endFigure 11: rule for FFT Transformer4. Alternative Models4.1 Variable Size Systolic ArraysOne limitation of the ELAN models presented aboveis that the rules are defined for a specific systolicarchitecture. A more flexible description will allow thespecification of systolic arrays with an arbitrary numberof functional units. In this case, the rewriting rulesshould be defined independently of the array size ortopology.This is exemplified in this section through the modeling of a simple version of the KressArray architecture [HaKrHe95]. It is defined by a matrix of reconfigurable functional units (rDPUs: reconfigurabledatapath units) where both the operations and the interconnections may be redefined (compare fig. 12 c and d). Figure 12 illustrates a KressArray family design space, which covers a wide variety of reconfigurable connect fabrics: nearest neighbour interconnect (NN) and backbus fabrics (segmented and / or non-segmented). Figure 13 shows a detailed example of NN ports featuring individual path width and individual mode (in, out, or bi-directional).Mapping C expressions to KressArrays is performed by assigning C operators to the nodeswhile keeping the corresponding data dependency among them. One particularity is that a KressArray is a pipe network which implements a dataflow model of computation. Coming along with synthesis tools also supporting non-uniform non-regular pipe networks [HHHN00, Na01] (in contrast to classical systolic array synthesis methods accepting only applications with strictly regular data dependencies) the KressArray family is a generalization of the systolic array. In addition to the generalized NN interconnect the KressArray family also provides abackbus (BB) second level interconnect fabrics with resources like buses and bus segments (for familymember examples see fig. 12 e, f, g).The DPU nodes of both, systolic arrays and rDPAs,may operate in a clocked mode, or asynchronously,where each operation is triggered as soon as data isavailable at the node inputs. (The latter version ofsystolic arrays has been usually called wavefrontarrays). This asynchronous operation is accomplishedby a handshake between interconnected nodes, sinceeach operation may take several clock cycles(multiplication, for instance, is implemented in itstypical serial way, through sums and shifts).Modeling of KressArrays in ELAN takes a different approach. To allow the specification of variable size systolic arrays, the nodes are stored on a list of arbitrary length. The designer provides the interconnections among nodes through signals, implemented with variables that connect the registers at the inputs and outputs of the nodes. Thus, if node n i is connected to node n j , then the same variable is associated to n i output and n j input. The operations of the nodes are dynamically specified along with the data that is to be processed by the array. To illustrate this kind of modeling lets consider a practical example: a KressArray that computes the differential equation loop body, given in figure 14.This array is defined by a list of 12 nodes, numbered from left to right and top to bottom. The first 4nodes are presented in figure 15. Each rDPU node is a kind of rAlu (reconfigurable Arithmetic-Logic Unit). In this simplified version, each rDPU has two registers in the inputs and one register at the output.Each register is defined by the variable it holds, its value and a flag that indicates if the data it holds is valid. The flag models the signal used for handshake in hardware. Rule assign() is used by the designer to provide values to input variables, specified in the form “x=5.y=2…”. Then, rule dpu() is applied to the Figure 12. KressArray family design space:(a, b) NN fabrics examples; (e, f, g) backbus (BB) fabrics examples; rDPU configuration:c) routing only configuration, d) routing and function configuration Figure 13: a KressArray family member example illustrating individual port mode and path width。

考研英语活学活用难点词

考研英语活学活用难点词部门： xxx时间： xxx整理范文，仅供参考，可下载自行编辑《考研英语活学活用2000难点词》Aabandon v. 放弃；抛弃［活学］desert抛弃give up放弃forsake遗弃discard丢弃quit舍弃leave dropabide v. 坚持，遵守［活学］abide by坚持，遵守comply with conform tokeep to stick toobey observeabdomen n. 腹，腹部［活学］belly腹部；胃thigh大腿liver肝脏guts肠kidney肾脏lung肺stomach胃limb四肢chest胸hip臀部bowel肠rib肋骨lap大腿waist腰部knee膝盖ankle踝wrist腕关节elbow手肘heel脚后跟paw爪abnormal a. 反常的，不正常的［活学］unnatural deviantirregular oddqueer 不正常的，反常的abolish vt. 废除，取消［活学］do away with废除，去掉discontinue scrap 废弃，报废cancel call off 取消(已安排的活动>eliminate淘汰(不需要的东西> abound vi. 大量存在；(in，with>充满，富于［活学］abound v. 充满abundant a. 充足的，富裕的pronounce v. 发…音pronunciation n. 发音found v. 建立fund n. 基金b5E2RGbCAPfundamental a. 根本的abrupt a. 突然的，意外的；(举止、言谈等>唐突的，鲁莽的［活学］rude crude 粗鲁的gross coarse 粗俗的rough粗野的，粗暴的wild野蛮的reckless鲁莽的bold冒失的rupt=breakerupt(尤指火山>爆发interrupt中断corrupt 腐败，堕落disrupt使中断absorb v. 吸收；吸引，使专心［活学］be absorbed in be immersed inbe preoccupied withbe engrossed in 专心于abstract a. 抽象的 n.摘要，提要 v.提(抽取>［活学］abstract摘要extract摘录summary概要，总结overview概述outline梗概，大纲sketch梗概，大意skeleton梗概，提要tract=pull abstract提取extract拔出，抽出distract使分心subtract减去tractor拖拉机absurd a. 荒唐的，荒谬的［活学］ridiculous illogicalsenseless unreasonable 荒谬的abundant a. (in>丰富的，充分的，充裕的p1EanqFDPw［活学］substantial liberalsufficient plentiful 丰富的abuse年 n. 滥用；辱骂 v. 滥用［活学］use使用apply应用utilize利用employ雇用avail 起作用take advantage of利用make use of利用resort toadopt 采用(手段>academy n. 学院［活学］school学校，学院college学院，大学conservatory音乐学院military institute军事学院arts school艺术学院accelerate v. 加速［活学］speed up step upput on a spur pick up speedquicken go fasterhasten 加速accent n. 腔调，口音；重音(符号>［活学］pronunciation发音intonation语调stress重音dialect方言access n. 接近，进入；入口(见inlet>；通路；接近(或进入>的方法DXDiTa9E3dacclaim vt. 向…欢呼，为…喝彩 n. 称赞，欢迎［活学］applause 鼓掌欢迎，欢呼cheer 喝彩hail 欢呼clap 鼓掌欢呼/欢迎accommodate v. 留宿，收容；供应，供给［活学］put up留宿house供宿lodge住宿，留宿provide sb.with sth.supply sb. with sth. 为…提供…accompany v. 陪同，伴随；为…伴奏［活学］escort 送护，护卫convoy 护送accomplish v. 完成［活学］achieve attaingain realize 达到，实现fulfil completecarry out 完成，实现accord n./v. 一致，符合 vt. 授予，赠与，给予［活学］accordance agreementconsistence 一致accordance n. 一致［活学］agreement harmonyaccord 一致accordingly ad. 因此，从而，相应地［活学］so thus hencetherefore consequentlyfor that reason as a resultin view of that 因此accountant n. 会计［活学］treasurer 司库，财务主管accountant 会计teller (银行>出纳cashier 出纳员，收银员accountancy 财务finance 理财banker 银行家treasury 国库，文库auditor 审计师accumulate v. 积累，积蓄，堆积［活学］amass collectgather heap hoardpile up build up 积累，堆积accurate a. 精确的，准确的［活学］precise exacttruthful 准确的acknowledge v. 承认；致谢［活学］admit allowconcede confessgrant 承认acquisition n. 获得；获得物［活学］attainment achievement acquirement 获得acre n. 英亩［活学］hectare公顷acrobat n. 杂技演员；善变者［活学］circus马戏comedy 喜剧circus performer 马戏演员相声acrobatics 杂技gymnast 体操运动员clown小丑magic 魔术，戏法magician魔术家trick恶作剧activate v. 使活动，启动［活学］set in motionstarttriggerget goingstimulate 启动acute a. 敏锐的，尖锐的；(疾病>急性的［活学］sharpkeensensitive 敏锐的acute/chronic disease急性/慢性病addict vt. 使成瘾，使入迷 n. 有瘾的人，入迷的人adhere v. 粘附，依着；坚持(见persevere>，遵守［活学］stick toglue to 粘附在…hold toadhere to 坚持，遵守cling to坚持，墨守keep to遵守，信守stand to恪守，遵守(诺言>stick to坚持，信守，忠于adjacent a. 邻近的，毗连的［活学］neighboringnearbyborderingnext (to>adjoining 毗连的adjoin v. 毗连，靠近［活学］connect连接affix粘上attach附上link up连起来borderbe next to 毗连administer v. 掌管，料理…的事务；实施，执行；给予，投(药>［活学］managerungovernoversee 掌管adolescent n. 青少年 a. 青春期的，青少年的［活学］teenagerteens 十几岁的青少年youngsterjunior 年轻人youth青年young adults青壮年adore vt. 崇拜，敬慕，爱慕；非常喜欢［活学］worship 崇拜admire 羡慕love 爱慕esteem 尊敬respect 敬重advent n. 出现，到来［活学］arrival 到来，到达introduction 引入，介绍adverse a. 不利的，有害的［活学］unfavorableundesirableharmful 有害的advocate v. 提倡，鼓吹 n. 提倡者，鼓吹者［活学］supportsponsorencouragebackback up 提倡aerial a. 空中的，航空的 n. 天线［活学］wavelength 波长band 波段channel 频道tune in 选台short wave 短波middle wave 中波aesthetic a. 审美的，美学的affection n. 爱，慈爱；感情；影响［活学］feelingsentiment 感情emotion情感passion热情，激情warmth 热情love爱情；恋爱fondness宠爱attachment 依恋affiliate v. 使隶属(或附属于> n. 附属机构，分公司［活学］subordinateassociatebelong toattach 隶属于affirm v. 断言，肯定，坚持声称［活学］assertconfirmclaimmaintain 断言，肯定affluent a. 富裕的，富足的［活学］richwealthy富裕的abundantsufficientenoughample 充足的prosperous 繁荣昌盛的agency n. 代理(处>，代办(处>［活学］office办事处affiliate 附属机构，分公司institutionestablishmentorganizationorgan 机构service 服务机构mechanism 机构，机制agenda n. 议事日程［活学］schemescheduleprogramtimetable 计划，安排，规划aggravate v. 恶化，加重，加剧［活学］worsenintensifydeteriorateweakenget worse 严重，加剧，恶化aggressive a. 侵略的，好斗的；敢作敢为的，有进取心的［活学］hostile敌对的，敌意的antagonistic对抗的，敌对的offensive冒犯的，无理的cruel残忍的，残酷的wild野蛮的，狂妄的violent猛烈的，强暴的fierce残忍的，凶猛的agitate v. 鼓动，煽动；搅拌［活学］exciteinciteprovokestir upwork up 激起，挑衅，煽动agony n. 苦恼，痛苦［活学］torturetormentanguish 折磨sufferingmiserypain 痛苦wrench(离别的>痛苦distress苦恼，危难，不幸adversity不利hardship艰苦agreeable a. 惬意的，令人愉快的；易相处的，同意的［活学］pleasantsatisfyingenjoyabledelightful 令人愉快的aisle n. 过道，通道［活学］passage 通道corridor 走廊album n. 粘贴簿，集邮簿，相册［活学］folder 折叠的小册子photo album 相册stamp album 集邮册alert a. 警惕的，警觉的；留神的［活学］attentivewatchfulvigilantcautiouswary 提防的，留神的alien n. 外侨，外星人 a. 外国的；相异的；不相容的［活学］strange外地的，异乡的foreign外国的incompatible不相容的allege v. 断言，宣称［活学］claim声称declare宣称assertaffirm 断言alleviate v. 减轻，缓解，缓和［活学］easelessenlightenrelieve 缓和，减轻allocate v. 分配，分派，把…拨给［活学］assignallotdistribute 分配alloy n. 合金［活学］metal金属aluminum铝gold金iron铁mercury汞nickle镍tin锡zinc锌calcium钙uranium铀ally n. 同盟国，同盟者，支持者［活学］partner合作者，合伙人associate合作人，伙伴，同事collaborator合作者supporter支持者companion同伴pal好友mate伙伴alliance结盟，联盟，联姻alter v./n. 改变，变更［活学］change 改变modify 更改transform 转变convert 变换，转化vary 变化，变更revise 修改，修订switch 转换shift 转换，替换alternate a. 交替的，轮流的 v. 交替，轮流［活学］substitutereplacetake the place of 替换，取代displace置换alternative n. 可供选择的事物，替换物，选择对象 a. 两者挑一的［活学］optionchoicesubstitute 选择对象altitude n. 高度，海拔［活学］heightelevation 高度ambassador n. 大使［活学］diplomat外交官envoy使节consul领事consulate领事馆ambiguous a. 模棱两可的［活学］vague模糊的unclear不清楚的confusing易混的indefinite不明确的indistinct不清楚的ambulance n. 救护车［活学］lorry运货卡车automobile汽车van客货两用车truck 载重汽车，卡车fire engine消防车cable car缆车sports car赛车amend v. 修改，修正［活学］revisemodify 修改alter改变，变更adjust校正amiable a. 和蔼可亲的，友好的［活学］graceful 个人风貌的温文尔雅gracious 上层对下层的和善amiable 和善、友好courteous 彬彬有礼hospitable 好客的benevolent 善意的merciful 仁慈的compassionate 富于同情心的agreeable 惬意的，易相处的心地善良的friendly 友好的sociable 爱交往的ampere n. 安培［活学］transformer变压器voltage电压volt伏特watt瓦，瓦特ample a. 充分的，富裕的［活学］sufficientadequateabundantplentyplentiful 足够的，充足的substantial富裕的amplifier n. 放大器，扩音器［活学］microscope显微镜loudspeaker扬声器microphone扩音器，话筒amplify v. 放大，增强［活学］intensify增强(效果> enlargemagnify 放大analogy n. 比拟，类比［活学］similaritylikeness 类似，相似parallel平行,类似simulation模拟equivalence等同correspondence对应comparison比较correlation关联ancestor n. 祖宗，祖先［活学］forefatherforerunner 祖先predecessordescendant 后代anchor n. 锚 v. 抛锚，停泊［活学］fastensecurefixaffix (使>固定anecdote n. 轶事，趣闻［活学］story 故事tale 传说yarn 奇闻漫谈，旅行轶事fable 寓言legend 传说fairy tale 童话myth 神话narrative 故事fiction 虚构、小说reportage 报告文学(auto>biography 自传/传记angle n. 角；角度，方面，观点［活学］perspectivestandpointapproachoutlookviewpoint 观点，角度anguish n./v. (精神或肉体的>极度痛苦［活学］。

中石油托福词汇频率

Cast anchor; cast down; cast forth; cast off; Cast-off>n.adj.
To supply food ready to eat for parties Any large and important church A large cave or chamber in a cave Hole; dental caries = tooth decay; Stop; interrupt; N. = end . Of heaven or the spirit; of or relating to the sky. celestial body; celestial equator; Viola; the bass member of the violin family. A count of the population Serials of acts prescribed by ritual, protocol, or convention Irratate; warm by rubbing; wear caused by friction Bedroom; enclosed space or cavity A state of utter confusion <> cosmos A charcoal drawing A written instrument; hire, rent, lease; charter school Castle or fortress; mansion Moderately cold>depression; lacking warmth of feeling 黑<>大 gorilla Used to chip, carve; cheat gallant or distinguished gentlemen Chop-mark; rough with small waves Accord, harmonize ; seventh chord; A large noteworthy quantity

小学上册第十五次英语第六单元测验卷

小学上册英语第六单元测验卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.I enjoy the sound of __________ when I’m inside. (雨)2.What is the main ingredient of the sun?A. OxygenB. HydrogenC. HeliumD. Carbon3.What do you call a story set in the future?A. Historical fictionB. FantasyC. Science fictionD. RomanceC4.What is the opposite of ‘safe’?A. SecureB. DangerousC. ProtectedD. Free5. A __________ day is good for hiking. (晴朗的)6.My dad loves to play ____ (cricket) with friends.7.I enjoy _______ (制作) videos.8.How many players are on a rugby team?A. 13B. 14C. 15D. 169.The pufferfish can inflate to avoid ________________ (捕食者).10.The ________ (城市发展) affects many people.11.What is the main source of energy for the Earth?A. SunB. WindC. WaterD. Fossil fuelsA12.The _______ (金鱼) swims gracefully.13.What is the currency used in the United States?A. EuroB. YenC. DollarD. PoundC14.The _____ (salad) contains many fresh ingredients.15.I want to _______ (learn) how to cook.16.Oxidation is a reaction involving the loss of _____.17.The __________ (纳粹党) led to World War II in Germany.18.The ancient Greeks made significant contributions to _______ and science.19.What is the opposite of "happy"?A. SadB. ExcitedC. AngryD. Tired20.The ____ is a small, colorful fish that lives in aquariums.21.The ______ helps us learn about social issues.22.The first settlers in America were looking for _______. (新机会)23.The _______ (鲸鱼) communicates with others through songs.24.The __________ is a large desert located in southern Africa. (卡拉哈里沙漠)25.The flowers smell very ___ (sweet).26.The __________ is a famous area known for its wildlife.27.The teacher instills a sense of _____ (责任感) in students.28.I like to ___ new things. (learn)29.The owl can turn its head _________. (很远)30.Mars rovers send back pictures and ______.31.The bat uses its _______ (回声定位) to navigate.32.I built a huge _________ (城堡) with my building blocks and it looks _________ (很棒).33. A _______ is the smallest unit of matter.34.I want to plant ________ in my bedroom.35.I enjoy _____ (写作) in my journal.36.The _____ (火烈鸟) is often seen in warm, shallow waters.37.What is the capital of Palau?A. NgerulmudB. KororC. MelekeokD. AiraiA38.When it's foggy, I need to drive __________. (小心)39.My aunt is a ______. She loves to teach children.40.What is the capital of Peru?A. LimaB. ArequipaC. TrujilloD. CuscoA41.I love to ________ stories.42.The gas produced when baking soda and vinegar react is __________.43.We like to ________ (play) outside.44.The fish is swimming in the ________.45.What is the main source of light for the Earth?A. MoonB. StarsC. SunD. FireC46.What continent is known as the "Dark Continent"?A. AsiaB. AfricaC. AustraliaD. EuropeB47.I think learning a new language is fun. I’m currently learning __________.48.What is the largest organ inside the human body?A. BrainB. LiverC. HeartD. LungsB49.What is the primary color of the sun?A. GreenB. BlueC. YellowD. RedC50.The _____ (小鸟) builds its nest high in the tree.51.The fish swims in ______ (水) gracefully.52.What is the main food that pandas eat?A. MeatB. FishC. BambooD. Grass53.What do bees make?A. MilkB. HoneyC. ButterD. Sugar54.The tree is _______ (full) of leaves.55.What do you call the place where you can buy snacks?A. StoreB. ShopC. MarketD. DeliA56.I like to play with my ________ (玩具名称) after school.57.The __________ (亚洲) is the largest continent in the world.58.She has a ______ cat. (black)59.I want to be a _____ when I grow up. (doctor)60.The ______ helps distribute nutrients in plants.61.What is the name of the famous American actor known for "The Godfather"?A. Al PacinoB. Robert De NiroC. Marlon BrandoD. Jack NicholsonC62.The chemical formula for water is ______.63.We will go to the _____ (zoo/museum) this weekend.64.The __________ is a major river in China. (长江)65.I like to explore the ______ (海滩) and look for beautiful ______ (贝壳).66.What is the term for a large body of freshwater surrounded by land?A. LakeB. PondC. RiverD. OceanA67.I want to paint my ________ bright red.68.Every morning, I write in my _______ (日记). It helps me organize my _______ (思想).69.The _____ (营养) from the soil is vital for growth.70.What is the term for a young eagle?A. ChickB. EagletC. HatchlingD. FledglingB71.I like to play ________ (视频游戏) with friends.72.The raccoon is known for its _______ (灵活).73.In a chemical reaction, reactants are transformed into ______.74.The capital of Turks and Caicos Islands is __________.75.What do we call a sweet food made from cream and sugar?A. Whipped CreamB. MousseC. Chantilly CreamD. All of the above76. A __________ is an area where two tectonic plates meet.77.We have a ______ (丰富的) menu for lunch.78.What do you call the part of the plant that absorbs sunlight?A. RootB. LeafC. StemD. Flower79.The clock ticks _____ (slowly/quickly).80.What is the color of grass?A. BlueB. GreenC. BrownD. Purple81.The __________ (历史的社会责任) encourage engagement.82.What is the opposite of "young"?A. OldB. NewC. FreshD. Recent83.What do we call the process of water falling from the sky?A. EvaporationB. PrecipitationC. CondensationD. Sublimation84.The __________ (历史与记忆) shape national identities.85.On weekends, I enjoy ______ (看电影) with my family. We often watch ______ (动画片) and eat ______ (爆米花).86.What is the capital of Lesotho?A. MaseruB. TeyateyanengC. MafetengD. Mohale's HoekA87.What do we call the sound a duck makes?A. QuackB. BarkC. MooD. Meow88.I enjoy playing with my toy ________ (玩具名称) in the garden.89.The dog is _____ with a ball. (playing)90. A mixture of oil and water is an example of a ______ mixture.91. A compound is a substance formed from two or more ______.92.The __________ blooms in spring.93. A base feels slippery and tastes _____.94.Space agencies work collaboratively on international ______.95.sustainable development) meets present needs without harming future generations. The ____96.How many wheels does a bicycle have?A. OneB. TwoC. ThreeD. Four97.What is the name of the first artificial satellite launched into orbit?A. Sputnik 1B. Explorer 1C. Vanguard 1D. Luna 198.What is the main ingredient in a taco?A. TortillaB. RiceC. BeansD. CheeseA99.I enjoy ________ in the garden.100.Plants are essential for ______ (生态平衡).。

八级词汇

abandon v 抛弃，放弃abnormal a 反常的，不正常的abolish v 废除，取消abortion n 流产，堕胎abrupt a 突然的，唐突的absence n 缺席，缺乏absolute a 绝对的，完全的abstract a & n 抽象的、摘要absurd a 荒唐的abundant a 充裕的，丰富的abuse v 滥用，虐待academy n 学会，专科学院accelerate v 加速access n & v 通道，入口，可接近、进入的权利；存取（计算机文件）accessible a 已接近的，可到达的accommodation n 住处，住宿accompany v 陪同，伴随accomplish v 完成，实现according a & ad(2013新增)按照, 依照（某事物）accountant n 会计（师）accumulate v 积累；积聚accuracy n 准确，精确accustomed a 习惯…的acknowledge v 承认，告知已收到acquaintance n 结识，熟人acquire v 取得，获得acquisition n 获得，习得acre n 英亩acute a 尖锐的; 剧烈的, 激烈的; 敏锐的; 严重的adapt v 适应，改编adaptation n 适应，改编本addicted a 上瘾的，入迷的addition n 加，加法adequate a 充分的，足够的adjust v 适应，调整adjustment n 适应，调整admirable a 令人钦佩的admission n 承认，允许进入n 青春期adolescent n 青少年adopt v 采纳，领养adore v 敬慕，钟爱advocate v 拥护，倡议affect v 影响，打动affection n 钟爱，喜爱agency n 代理处，代办处agenda n 议事日程agent n 代理人，经纪人aggressive a 好斗的，有进取心的agricultural a 农业的agriculture n 农业alarm n & v 警报，惊慌，使惊慌album n 相簿，专辑alcoholic a & n 含酒精的，嗜酒者algebra n 代数alley n 胡同，小巷allocate v 分配，把…拨给allowance n 津贴，补助alongside ad 并排/肩地alternative a 供选择的，可替代的altitude n 高度，海拔aluminium n 铝amateur a 业余的ambiguous a 模棱两可的ambition n 雄心，野心ample a 充分的，丰裕的amuse v 逗笑，使…娱乐anchor v & n 锚，抛锚anecdote n 轶事anniversary n 周年（纪念日）annual a 每年的，一年一次的antique n 古董，古玩apart ad & a 分开、相距apparent a 明显的，显而易见的appeal v & n 呼吁，上诉，吸引appendix n 附录，阑尾appetite n 食欲，胃口，爱好applaud v & n 鼓掌，喝彩applicant n 申请人，应征者appoint v 指定，任命appreciation n 欣赏，感谢appropriate a 适当的approval n 赞同，批准approve v 赞同，批准arbitrary a 专断的，任意的arch n 拱门，弓形结构architecture n 建筑学，建筑assess v 评价，估价assessment n 评价，估价assist v 帮助，援助assistance n帮助，援助associate v联系，联想assume v 假定，假装，呈现assumption n 假定，承担，就任astonish v 使惊讶athletic a 运动的attain v 达到，获得attend v 出席，参加，照料attraction n 吸引（力）authentic a 真正的，可靠的authority n 权威，官方autonomous a 自制的awesome a 使人敬畏的，可怕的awkward a 使人尴尬的Bbachelor n 单身汉，学士bacterium (pl bacteria) n 细菌bakery n 面包店balcony n 阳台ballet n 芭蕾舞bandage n 绷带barber n 理发师barbershop n 理发店bare a 赤裸的，光秃的barrier n 障碍，屏障bay n 海湾bean curd n 豆腐beddings n 床上用品behalf n 代表being n 存在，人belly n 肚子beneficial a 有益的bent a & n 弯曲的/爱好，倾向betray v 背叛，流露bid v & n 出价，投标bingo n 宾戈biochemistry n 生物化学biography n 生物学bishop n 主教bless v 祝福，保佑bond n & v 联系、纽带；使结合，黏合boom n & v 岗，亭border n 边界botanical a 植物学的botany n 植物学bounce v 弹起，反弹bound a 一定会，很有可能会boundary n 边界，界限bow v & n 鞠躬，弓形物boycott v 抵制bravery n 勇敢breakthrough n 突破brewery n 酿造厂brick n 砖块brochure n 小册子，说明书brunch n 早午餐Buddhism n 佛教buffet n 自助餐bungalow n 平房burden n 负担bureaucratic a 官僚的burst vCcab n 出租车cafeteria n 自助餐厅calculate v 计算，推测，打算campaign n 战役，运动canal n 运河，水道candidate n 候选人，参加考试的人capsule n 胶囊，太空舱caption n 字幕，说明文字carbon n 碳carrier n 搬运人，运输公司，带菌者carve v 雕刻cast (cast, cast）v 投，抛，catalogue n 目录catastrophe n 大灾难category n 种类，范畴cater v 迎合，满足catholic a 天主教的caution n 谨慎，告诫celebration n 庆祝cell n 细胞，单人牢房certificate n 证书changeable a 易变的，变化无常的chaos n 混乱characteristic a 特有的，独特的choir n 唱诗班，合唱团choke n & v使窒息，阻塞chorus n 合唱，齐声Christian n 基督教徒circuit n 环行，巡回，电路，线路circulate v 循环，流传，传播circumstance n 情况，形势civilian n 平民，百姓clarify v 澄清，阐明classify v 将…分类claw n 爪clay n 泥土click v 点击，发出咔嗒声clumsy a 笨拙的，不灵活的coincidence n 巧合（的事）colleague n同事collection n收集（物）收藏（品）collision n碰撞事故；冲突combine v（使）结合，（使）联合comedy n喜剧command n & v命令；指挥commercial a商业的，商务的，商品化的commit v(to) 使作出保证，承诺；犯（错误、罪行）；投入（钱、时间等）commitment n承诺，保证；献身，投入communism n共产主义communist n & a共产主义者，共产主义的community n社区，社会；团体，界；(动植物的)群落comparison n比较，对照；比拟compass n罗盘，指南针；圆规compensate v competence n(for)补偿，赔偿complex a & n复杂的，复合的；联合体，情结component n组成部分，部件，零件compromise v妥协，折中，让步compulsory a义务的，强制的；必修的concrete a具体的，有形的(反：abstract); n 混凝土condemn v 谴责，指责；宣告有罪，判刑confidential a秘密的，机密的conflict n战斗，斗争；冲突，抵触conscience n良知，良心consensus n一致意见，共识conservation n保存；（对自然资源的）保护，节约conservative a保守的，守旧的n保守主义者considerate a考虑周到的，体贴的consideration n考虑，体贴，关心consist v(of)由…组成；由…构成；(in) 在于consistent v(with)一致的，一贯的；稳定发展的，持续不变的construct v建造，建设，构造consultant n顾问，会诊医师consume v消耗，消费；吃，喝container n容器，集装箱contradict v反驳，与…矛盾/抵触contradictory a相互矛盾的contrast v & n 对比；反差；对比vi.(with)形成对比controversial a引起争议的，有争议的conventional a惯例的，常规的，守旧的convey v搬运，运送；转达，表达convince v(of) 说服，使信服correspond v(to) 相当于；(to,with)符合，一致；(with)通信corrupt a & v腐败的，贪污的；贿赂，(使)腐败counter n柜台，计算器crash n & v（车辆）碰撞，（飞机）坠落；撞坏；失败；撞击（声）；爆裂（声）；失败，瓦解cream n奶油；乳脂criterion （pl criteria）n标准，准则crossing n十字路口，人行横道cube n立方形/体cubic a立方形/体的cuisine n烹饪（法）cure n & v治愈；消除，解决curious a好奇的；稀奇的，奇妙的currency n货币；流通curriculum n（学校的全部）课程cushion n垫子customs n关税；a海关的Ddam n 水坝，水堤dash v & n（猛）冲，突进，飞奔，短跑database n资料库，数据dawn n黎明，拂晓（反：dusk）;开端deadline n最后期限，截止日期debate n & v辩论，争论decade n 十年declare v宣布，声明，断言decline v减少，下降，衰退；拒绝，谢绝decoration n装饰，装潢delay n & v延迟，耽搁，拖延delete v & n删除deliberately ad故意地delicate a纤弱的；精致的；微妙的，优雅地delight n快乐；乐事v使快乐deliver v递送，发表；释放departure n离开，启程（反：arrival）deposit v & n使沉淀；存放，储存；付（保证金）；沉积物；存款；保证金depth n深，深度desperate a绝望的；不顾一切的，拼死的destination n 目的地，终点diagram n图解，图表digest v消化，领会n摘要，文摘digital a数字的，数码的dignity n庄严，端庄；尊贵，高贵dilemma n（进退两难的）窘境，困境dimension n尺寸，尺度；维（数）dioxide n二氧化物diploma n 毕业文凭，学位证书disappoint v使失望discourage v使泄气；阻止discrimination n 歧视disgusting a 令人作呕的，使人讨厌的distribute v 分发，分配；分布disturbing a令人不安的diverse a多种多样的dizzy a头晕目眩的donate v 捐赠，赠送dot n（圆）点download n & v下载（反：upload）draft n & v草图，草稿，草案；起草，草案，草拟drawback n欠缺，缺点due a到期的；预期的，约定的dull a单调乏味的；阴暗的；迟钝的dynamic a有生气的；动力的，动态的dynasty n王朝，朝代Eeager a渴望的，热切的ecology n生态（学）edition n版本；（发行物的）版次effect n结果，效果，作用elect v选举；选择，决定electronic a电子的elegant a高雅的，优雅的，文雅的emperor n皇帝ending n结尾，结局endless a无穷无尽的engage v吸引，占用；聘；使订婚；(in)从事于enlarge v扩大enquiry n = inquiry询问enterprise n 进取心，事业心；企/事业单位;事业entertainment n娱乐entry n进入；入口处equality n平等equip v (with) 装备，配备erupt v（尤指火山）爆发；突然发生evaluate v评估，评价eventually ad终于，最后evident a明显的，显然的evolution n演变，进化，发展expand v（使）膨胀；（使）扩张；张开，展开expense n费用，开支explicit a明确的，坦率的（反：implicit）explore n 探测，勘探；探索，探究expose v (to) 使暴露，使曝光extension n延长，伸展，扩大Ffade v 褪色；变微弱faith n 信仰；信任fancy n, v & u 想象（力）；幻想a.花式的；奇特的fantasy n 想象；幻想fasten v 使牢固；拴住，扎牢feast n 宴会；大餐，盛宴federal a 联邦（政府的）ferry n 渡船fibre （Am fiber）n 纤维fiction n 小说；虚构，想象的事figure n 外形；图形；数字；（人的）身材；人物；雕像v 计算；以为，认为；揣测finance n 财政，金融资金vt 为……提供资金financial a (2013新增) 财政的；金融的fingernail n 手指甲fireworks n 焰火flee (fled, fled) v 逃走，逃避flexible a 易弯曲的，柔韧的；灵活的float v 漂浮；飘动fluency n.流利，流畅forbid (forbade, forbidden）v 禁止，不许foresee（foresaw, foreseen）v 预见，预知forgetful a 健忘的；不经心的fountain n 泉水，喷泉fragile a 易碎的，脆的fragrant a 芬芳的，香的framework n 框架，构架freezing a 结冰的，极冷的friction n 摩擦（力）frontier n 边境，国界；前沿，前线fund n (2013新增) 资金，基金v.提供资金fundamental a 基本的，基础的funeral n 葬礼furnished a 配备了家具的Ggallery n 美术馆，画廊gallon n 加仑（液量单位）garment n 衣服gather v 聚集；采集，收集gay a 快乐的，愉快的；同性恋geometry n 几何glance v 匆匆一看，一瞥glare v 怒视，瞪眼；（发出）强光globe n 球；地球仪【th e～】地球goal n 目标；（足球）球门goods n 商品，货物govern v 统治，管理graph n 图标，曲线图grateful a （to，for）感激的，感谢的gravity n 重力，地心引力greet v 问候，迎接，招呼grill n 烤架growth n 生长，增长guarantee v/n 保证(书)，担保Hhaircut n （男子）理发handful n 一把；一小撮，少数handy a 手边的，近便的；手巧的，灵活的hardship n 艰难，困苦harmony n 协调，和谐，融洽hatch v 孵出，孵化headline n 大字标题herb n 药草，香草holy a 神圣的hook n 钩v钩住；衔接，连接hydrogen n 氢Iidentification n 身份证明；鉴定，识别ignore v 不顾，不理；忽视immigration n 移民入境impact (2013新增) n 冲击力，撞击，影响，作用v 冲击，产生影响import v & n 进口；输入impress v 印；留下印象infer v (2013新增) 推论出，推断inform v （of，about）通知，告诉initial a 开头的，最初的institution n. 建立，慈善机构intend v. 打算，想要interval n. 间隔，停顿involve v.(13新增) 需要，包括，牵涉irrigation n. 灌溉，冲洗issue n.&v. （13新增）放出，发出，争端，发行item n.(13新增) 条款，项目，一条，一件item n.(13新增) 条款，项目，一条，一件Jjet n. 喷气飞机，喷射jog n.& v. 轻推，慢跑jungle n. 丛林，混乱复杂的事物，发生混乱斗争的地方Llack n.&vt. 缺乏，不足lame a&vt. 瘸的，无说服力的lantern n. 灯笼，天窗latter a. 后期的，末期的laundry n. 洗衣店/房，洗熨好的/待洗的衣物league n. 联盟，范畴v. 联合liberty n. 自由，自主liberation n. 解放librarian . n. 图书管理员likely adj.很可能的link n.&. 环，圈，联系，连接loaf n. 大面包v. 虚度光阴lounge n. 休息室，等候室，起居室Mmaid n. 女仆，侍女，姑娘manner n 方式，方法，态度maple n.枫树marathon n. 马拉松marble n.大理石，玻璃弹球mask n&v. 面具，口罩；遮住mass n. 团，块，大量matter n. 事情，情况，物质v.关系重大，要紧mature a. 成熟的，深思熟虑的maximum a&n. 最高的，最大的，最强的，最大的量means n. 手段，方法meanwhile adv. 同时，其间media n. 大众传播媒介medium n. 媒介，介质，方法，手段melon n.瓜merchant n. 商人merciful a. 仁慈的，宽容的merely ad. 仅，只，不过mess n. 杂乱，不整洁的人messy a. 凌乱的，脏的microscope n. 显微镜microwave n. 微波minimum a. 最小的，最少的，最低限度的minister n. 部长，外交使节ministry n. (政府的)部mobile a. 易于快速移动的，有交通工具的monument n.纪念馆/碑/像mood n.(13新增)心境，情绪mop n.&v. 拖把，擦洗Moslem n. Moslim 穆斯林motivation n. 动机motor n. 发动机，马达，汽车motto n. 箴言，格言，座右铭mountainous n. 多山的，巨大的mourn v.哀悼musical a.&n. 音乐的，音乐喜剧mutton n.羊肉mustard n.芥末，芥末黄Nnavy n. 海军negotiate v.商议，谈判，协商noble a. 贵族的，高贵的，卓越的neutral a.(13新增) 中立的，公平的，无明显Ooffshore a. 近海的oilfield n. 油田omelette n. 煎蛋卷；煎蛋饼opener n. 开具，启子opening n. 开放，口子opera n. 歌剧opera house n.歌剧院，艺术剧院orbit n. （天体等的）运行轨道organ n.（人，动物）器官organiser (organizer) n. 组织者Ottawa n. 渥太华ouch int（突然受痛时叫声）哎哟outcome n. 结果，效果ownership n. 所有制Ppacket n. 小包裹，袋paddle n. 浆状物，蹼pan n. 平底锅pancake n. 薄煎饼parallel n. 极其相似的人；纬线parcel n. 包裹pardon n. 原谅，宽恕，对不起participate v.参加，参与particular a. 特殊的，个别的partly ad. 部分地，在一定程度上passer-by n. 过客，过路人passive a. 被动的patent n. 专利权，专利证书pause n.& vi. 中止，暂停；停止peasant n. 农民，佃农pedestrian n. 步行者，行人pencil-box n. 铅笔盒penfriend n. 笔友pension n. 养老金per prep. 每，每一perform v. 表演；履行，行动performance n. 演出，表演performer n. 表演者，执行者personnel n. 全体人员，职员pest n. 害虫pianist n. 钢琴家perfume n. 香味, 芳香; 香料; 香水pin n. v. 别针v. 别住, 钉住pint n. （液量单位）plot v. / n. 品脱plug n. 塞子vt.（用塞子）把…塞住poison n. 毒药poisonous a. 有毒的，致命的pole n.杆，电线杆the North (South) Pole（地球的）极，极地北（南）极polish v.擦亮n.擦光剂,亮光剂politician n. 政治家politics n. 政治porridge n. 稀饭，粥portable a. 手提的，便携的porter n. （火车站或旅馆处的）搬运工potential a. 潜在的，可能的prairie n. 大草原pray v. 祈祷；祈求prayer n. 祈祷precious a. 宝贵的，珍贵的precise a. 准确的，精确的，确切的predict v. 预言，预告，预报preference n. 选择，去向pregnant a. 怀孕的prejudice n. 偏见，成见premier n. 首相，总理preparation n准备presentation n. 介绍, 赠送, 陈述；演出preserve v. 保护，保留，保存primary school 小学primitive a. 原始的，远古的principle n. 道德原则，法则printer n. 打印机printing n. 印刷，印刷术privilege n. 特权，特殊待遇probable a. 很可能，很有希望procedure n. 程序，手续，待遇profession n.（需要有高等教育学位的）职业（如医生或律师）promote v. 促进，推动，促销，晋升psychology n. 心理学publicly ad. 当众；公开地punctual a. 准时的punctuate v. 加标点punctuation n.标点符号purchase v. 购买，采购pure a. 纯的，不掺杂的puzzled a. 迷惑的，困惑的pyramid n. 角锥形，金字塔Qquake n.& v. 震动，颤抖qualification n. 资格，学历questionnaire n. 调查表，问卷queue n. 行列，长队quilt n.被子，被状物quit v. 离任，离校，戒掉Rracial a. 种族的radiation n. 放射，放射物radioactive a.放射性的radium n. 镭rag n. 破布，抹布rail n. 铁路rainfall n. 一场雨；降雨量random a. 随意，未经事先考虑range n./ v. 变化，变动，排序rare a. 稀有的, 罕见的;杰出的, 珍贵的rate n. 比率;速度, 速率v.对...估价;评价rather ad. 相当，宁可raw a. 生的，未煮过的，未加工的ray n. 光辉，光线razor n. 剃须刀rebuild vt. 重建reception n. 接待receptionist n. 接待员recipe n. 烹饪法，食谱recommend v.推荐rectangle n. & a. 长方形，长方形的refer vi. 谈到，提及，涉及，有关referee n. 裁判，仲裁，调解员reference n. 提到,涉及,谈及,查询reflect v. 反映，反射reform v./ n. 改革，改进，改良refresh v. 使恢复精力，提醒refrigerator n. 冰箱regards n. 问候，致意regardless a. 不顾，不加理会register n. / v登记簿，花名册，注册员；登记，注册regulation n. 规则，规章reject v. 拒绝relate vi. 有关，涉及relay n / v接力，接替人；接替，补充release n / v 释放, 解放; 赦免; 豁免; 发行, 发表relevant a. 紧密相关，有意义的religion n. 宗教religious a. 宗教的remark n. 陈述，话，议论represent vt. 代表representative n.代表，典型人物reputation n. 名声，名誉request n. 请求，要求的事物rescue vt. 营救，援救resemble v. （不用进行时）像，看起来像reservation n. 预定reserve n. & v. 储备，预定resign v.辞职resist v. 抵抗，挡开restrict v. 限制restriction n. 限制，约束revolution n. 革命，变革rewind v. 回转（磁带等）rhyme n. & v. 押韵rid (rid, rid / ridded, ridded) vt. 使摆脱ridiculous a. 荒谬的，愚蠢的rigid a. 坚硬的，不易弯曲的，坚固的，严格的ripe a. 成熟的，熟的ripen v. 成熟restrict v.限制，约束restriction n. 限制, 约束revolution n. 革命, 变革rewind v. 回转; 重绕rhyme n. &v. 韵, 押韵rid (rid, rid or ridded, ridded) v. 使摆脱ridiculous adj. 荒谬的, 可笑的rigid adj. 刚硬的, 刚性的, 严格的ripe adj. 成熟的, 熟的ripen v. 成熟rob v. 抢夺, 抢劫roll v. 滚动, 打滚n. (一)卷, 卷形物, 摇晃, 摆动, 名单rooster n. 公鸡root n. 根, 根源, 起源rot v. 烂; 腐败rough adj. 粗糙的, 粗略的roundabout adj. 迂回的, 转弯抹角的n. 道路交叉处的环形路, 兜圈子的话routine n. 常规, 日常事务, 程序royal adj. 王室的, 皇家的rugby n. 橄榄球ruin v.（使）毁坏;（使）毁灭n. 毁灭, 崩溃, 废墟, 遗迹rural adj. 农村的Ssacred adj. 庄严的, 神圣的sacrifice v. 牺牲n. 牺牲salute v.& n.行礼致敬, 敬礼saucer n. 茶碟, 茶托, 小圆盘scan v. 细看, 审视, 浏览, 扫描scar n. 伤痕, 疤痕scare v. 惊吓, 受惊, 威吓sceptical/skeptical adj. 怀疑性的,好怀疑的scold v. 责骂scratch n. 乱写, 刮擦声, 抓痕v. 乱涂, 抓sculpture n. 雕塑, 雕刻作品seagull n. 海鸥seal n. 海豹, 封条, 印v. 封, 密封seashell n. 海贝seaweed n. 海草, 海藻security n. 安全seize v. 抓住, 逮住, 夺取semicircle n. 半圆seminar n. 研究会, 讨论发表会sentence n.句子, 判决, 宣判v. 判决, 宣判separation n. 分离, 隔离session n. 会议, 开庭settlement n. 新拓居地; 部落, 村落settler n. 移居者, 开拓者severe adj. 严厉的, 严重的, 严峻的shabby adj. 破旧的, 破烂的sharpen v.（使）变锐利, 削尖sharpener n. 削刀, 磨床shaver n. 剃须刀shelter n. 掩蔽; 隐蔽处shortly adv. 不久shot n. 射击, 开枪, 开炮, 射击声shrink (shrank, shrunk or shrunk, shrunken) v. 收缩, 缩短shuttle n. 往返汽车(列车、飞机), 航天飞机sideroad/sidewalk n. 人行道sideway n. 岔路, 旁路; 小路, 人行道sideways adv. 斜向一边; 向侧面地signature n. 签名significance n. 意义, 重要性sincerely adv. 真诚地skateboard n. 冰鞋, 滑板ski n. 滑雪板v. ; 滑雪skip v. 跳, 蹦n. 跳跃skyscraper n. 摩天楼slice n. 片, 切面（薄）片slide n. 幻灯片, 滑道v. 滑行, 滑动slight adj. 轻微的, 细小的slim adj. 苗条的, 纤细的slip n. 滑落；跌跤; 片, 条smog n. 烟雾sneaker n. 运动鞋sneeze v. 打喷嚏sniff v. 用力吸, 嗅, 闻到, 发觉, 轻视sob n.& v. 抽泣, 啜泣socialism n. 社会主义socialist adj. 社会主义的socket n. 窝, 穴, 孔, 插座solar adj. 太阳的, 日光的sorrow n. 悲伤, 悲痛soul n. 灵魂; 心灵; 气魄souvenir n. 纪念品, 纪念物spade n. 铲子spear n. 矛, 梭镖specialist n.专家; 专业人员specific adj. 详细而精确的, 明确的spin v.纺, (使) 快速旋转; n. 旋转, 旋转运动spiritual adj. 精神的; 心灵的split v. 撕开; 切开sponsor n. 发起人, 主办者, 保证人spoonful n. 一匙（的量）spray n. 水雾, 喷雾, 飞沫v. 喷射, 喷溅squeeze n. 压榨, 挤stable adj. 稳定的staff n. 全体职员stain n. 污点, 瑕疵stainless adj. 纯洁的, 无瑕疵的, 不锈的starvation n. 饥饿; 饿死starve v. 饿死statesman/woman (pl. statesmen /women) 政治家, 国务活动家statistics n. 统计学, 统计表statue n. 雕像, 铸像, 塑像steward n.男服务员; 男乘务员stewardess n. 女乘务员, 空中小姐stocking n. 长统袜storage n. 贮藏; 储存stout adj. 矮胖的, 结实的, 顽强的straightforward adj. 正直的, 坦率的, 直接了当的strait n. 海峡strategy n.战略；策略；计谋strength n. 力量, 力气strengthen v. 加强, 增强stress n. 压力, 重点, 重音v. 着重, 强调, 重读string n. 线, 细绳, 一串, 一行stubborn adj. 顽固的, 固执的, 坚定的, 坚决的, 难应付的, 难处理的studio n. 工作室, 演播室style n. 风格, 时尚, 文体subjective adj. 主观的, 个人的submit v. 提交, 递交subscribe v. 捐款, 订阅substitute n. 代用品, 代替者suck v. 吸吮suffering n. 痛苦, 苦难suite n. .(一批)随员, (一套)家具, 套房, 套, 组sunburnt adj. 晒黑的superb adj. 庄重的, 堂堂的, 华丽的, 极好的superior adj. 较高的, 上级的, 上好的, 出众的n.长者, 高手, 上级supreme adj. 极度的, 极大的, 至高的, 最高的surplus n. 过剩; 盈余；余款surgeon n. 外科医生surround v. 围绕; 包围survey n. 调查; 民意调查; 调查报告; v. 调查, 测量,survival n. 生存, 幸存suspension n. 暂停, 中止swap v. 交换swear (swore, sworn) v. 诅咒swift adj. 快的, 迅速的swing v. 摇摆, 摆动n.秋千, 摇摆, 摆动switch v. 转换, 转变n.开关, 电闸, 转换sword n. 剑, 刀sympathy n. 同情, 同情心symphony n. 交响乐, 交响曲symptom n. 症状; 表现; 征兆systematic adj. 系统的, 体系的Ttablet n. 药片tailor n. 裁缝talent n. 天才, 才干tank n. 坦克; 箱、罐target n. 目标, 对象, 靶子tasteless adj. 无滋味的taxpayer n. 纳税人teamwork n. 合作, 协同工作teapot n. 茶壶tease v. 揶揄, 戏弄, 逗惹technical adj. 技术的, 工艺的technique n. 技术; 技巧, 方法telescope n. 望远镜temple n. 庙宇, 寺院temporary adj. 暂时的, 临时的, 临时性tend v. 趋向, 往往是; 照管, 护理tendency n. 趋向, 倾向tense adj. 紧张的tension n. 紧张, 压力tentative adj. 试验性的, 试探的, 尝试的, 暂定的terminal adj.终点站; 终端terrify v. 使人感到恐怖terror n. 恐怖; 骇惧thankful adj. 感谢的, 感激的theft n. 偷, 行窃, 偷窃的事例, 偷窃行为theme n. 主题theoretical adj. 理论的theory n. 理论thermos n. 热水瓶thinking n. 思索; 见解; 想法thirst n. 渴; 口渴; 渴望, 热望thorough adj. 彻底的threat n. 恐吓, 威胁,thrill n. 兴奋；激动v. 使激动；使胆战心惊thriller n. 使人毛骨悚然的东西throughout prep. 遍及, 贯穿thunderstorm n. 雷雨；雷暴雨tight adj. 紧的tin n. 罐头, 听头tip n. 顶端, 尖端; 告诫; 提示v. (给)小费tire v. 使疲劳tiresome adj. 令人厌倦的tissue n. 组织；薄的纱织品, 薄纸tolerate v. 忍受, 容忍topic n. 题目, 话题tortoise n. 乌龟tough adj. 坚硬的; 结实的; 棘手的, 难解的tourism n. 旅游业; 观光tournament n. 比赛, 锦标赛, 联赛track n. 轨道; 田径tractor n. 拖拉机tram n. 有轨电车transform v. 转换, 改变, 改造, 使...变形transparent adj. 透明的; 透光的trap n. 陷阱v. 使陷入困境treat v. 对待, 看待tremble v. 颤抖trend n. 倾向, 趋势trial n. 审判; 试验; 试用trunk n. 树干; 大箱子；象鼻tube n. 管, 管子tune n. 曲调, 调子turkey n. 火鸡turning n. 拐弯处, 拐角处twist v. 扭弯, 扭曲, 缠绕n. 扭曲, 曲折typical adj. 典型的, 象征性的typhoon n. 台风Uunable adj. 不能的, 不能胜任的unbearable adj. 无法忍受的, 承受不住的unbelievable adj. 难以置信的uncertain adj. 不确定的uncomfortable adj. 不舒服的, 不安的, 不合意的unconditional adj. 无条件的, 绝对的, 无限制的unconscious adj. 未发觉的,无意识的underline v. 在...下面划线undertake (undertook, undertaken) v.承担, 担任, 许诺, 保证；答应；同意underwear n. 内衣unemployment n. 失业, 失业状态unfit adj. 不合宜的, 不相宜的unfortunate adj. 不幸的unfortunately adv.不幸地union n. 联合, 联盟; 工会unique adj. 唯一的, 独特的unite v. 联合, 团结universal adj. 普遍的, 全体的, 通用的, 宇宙的, 世界的unlike prep. 不像, 和…不同unrest n. 不安; 骚动unwilling adj. 不愿意的, 勉强的update v. 使现代化, 修正, 校正, 更新n.修正, 校正, 更新upper adj. 较高的, 较上的upset v. 扰乱, 使心烦adj. 心烦的, 苦恼的upward(s) adv. 向上; 往上urban adj. 城市的, 市内的urge v. 催促, 力劝urgent adj. 急迫的, 紧急的Vvacant adj. 空的, 空白的vague adj. 含糊的, 不清楚的vain n. 自负的, 自视过高的, 徒劳的, 无效的valid adj. 有效的valley n. 山谷, 溪谷variety n. 变化, 多样性, 种种, 种类version n. 译文; 版本vertical adj. 垂直的, 直立的via prep. 经, 通过, 经由11victim n. 受害人, 牺牲者videophone n. 可视电话violate v. 违反, 妨碍, 侵犯violence n. 暴力行为violinist n. 提琴家, 提琴手virtue n. 美德, 正直的品行, 德行virus n. 病毒visa n. 签证vital adj. 生死攸关的, 重大的vivid adj. 生动的, 鲜明的voluntary adj. 自动的, 自愿的, 主动的volunteer n 志愿者, 志愿兵v.自愿vote v. 选举, 投票Wwag v. 摇摆, 摇动; 上下移动walnut n. 核桃, 胡桃ward n. 病房, 牢房warehouse n.仓库；货栈warmth n.暖和, 温暖; 热烈wax n.蜡wedding n.婚礼weed n.杂草, 野草weekly adj.每周的adv. 每周一次weep (wept, wept) v. 哭泣, 流泪welfare n.幸福, 福利westward adj.西方的, 向西的adv.向西widow n.寡妇wipe v. 擦, 揩, 擦去withdraw v. 收回; 撤回; 撤退witness n.证据; 证人v. 目击woollen adj.羊毛制的, 毛线的worn a. 磨损的, 疲倦的worthwhile adj. 值得做的, 值得出力的worthy adj. 有价值的, 应...的, 可敬的, 值得的, 相称的wrestle v.摔跤, 格斗wrinkle n. 皱褶, 皱纹Yyawn v.打呵欠yell v. 大叫, 忍不住笑, 呼喊Zzipper n. 拉链zone n. 区域; 范围2014新增的词汇（27个）：complain v. 投诉，抱怨complaint n.抱怨，投诉，控告criticize v. 批评，挑剔current a.现在的; 现行的; 通用的; 通行的; 被普遍接受的n.（水﹑气等的）流, 流动；趋向, 趋势, 倾向definitely ad. 明确地; 清楚地；肯定地; 是的, 当然despite prep.尽管; 不管; 不顾detect v.觉察，侦查device n. 装置，器具；手法，技巧display v.&n. 展示，展览efficient a.能胜任; 有能力的；有效力的emphasize v.强调essential a. 必要; 不可缺少; 最重要本质的;基本的n.要素; 要点estimate n. & v.估计; 估价，判断feature n.特色; 特点；特写或专题节目v. 由（某人[某物]）主演gap n. 缺口，间隔image n.肖像,形象install v.安装；安置invest v. 投资investigation n. 调查，审问investment n. 投资opportunity n.机会，良机priority n. 优先，居要位sign n. 招牌，指示牌，示意，迹象v.打手势solution n. 解决办法solve v. 解决，解答survey n. & v. 调查threat n. 恐吓，威胁，预兆12。

我心目中农场作文英语

我心目中农场作文英语Farms have always held a special place in my heart. Growing up in a bustling city, I often found myself longing for the tranquility and simplicity of rural life. As I've grown older, my appreciation for the vital role farms play in our society has only deepened. In my mind's eye, the perfect farm is a harmonious blend of tradition and innovation, where the timeless rhythms of nature coexist with the latest advancements in sustainable agriculture.At the heart of my vision for an ideal farm is a deep respect for the land and a commitment to responsible stewardship. I envision a property where the soil is nurtured and cared for, where every acre is treated as a precious resource to be cultivated with reverence and skill. The farmers who tend to this land would be passionate stewards, guided by a profound understanding of the delicate balance of ecosystems and a steadfast determination to leave the earth in better condition than they found it.One of the key features of my dream farm would be its emphasis on biodiversity. Rather than vast monocultures of a single crop, I see atapestry of diverse plantings – a symphony of fruits, vegetables, grains, and flowers that work in harmony to support a thriving webof life. Hedgerows and wildflower meadows would dot the landscape, providing vital habitats for pollinators and other beneficial insects. Integrated pest management strategies would be employed, minimizing the need for harmful chemicals and fostering a natural balance within the farm's ecosystem.Sustainability would be a guiding principle in every aspect of the farm's operations. Solar panels and wind turbines would harness the power of renewable energy, reducing the farm's carbon footprint and contributing to a cleaner, greener future. Water conservation would be a top priority, with efficient irrigation systems, rain catchment, and wetland restoration projects ensuring that this precious resource is used responsibly. Waste would be minimized through composting, recycling, and the implementation of circular economy principles, transforming what was once considered trash into valuable inputs for the farm's nutrient cycle.At the same time, I envision my ideal farm as a hub of innovation and technological advancement. State-of-the-art precision farming techniques would be employed, using data-driven analytics and cutting-edge sensors to optimize crop yields, minimize resource use, and enhance overall efficiency. Robotic systems and autonomous vehicles would assist in the day-to-day tasks, freeing up the farmersto focus on the more nuanced and creative aspects of their work. Vertical farming and hydroponics would be integrated into the landscape, allowing for the production of high-quality, year-round crops in a compact, resource-efficient manner.But beyond its technological prowess, this farm would also be a place of community and connection. I envision a vibrant agritourism program, where visitors can immerse themselves in the rhythms of farm life, learn about sustainable agriculture, and forge a deeper appreciation for the origins of their food. Educational programs and workshops would be offered, empowering people of all ages to become more engaged with the natural world and the processes that sustain us.The farm's bounty would be shared not just with those who visit, but with the surrounding community as well. A robust network of farmer's markets, community-supported agriculture (CSA) programs, and partnerships with local businesses would ensure that the farm's high-quality, nutrient-dense produce is accessible to all, regardless of socioeconomic status. The farm would also serve as a hub for food justice initiatives, working to address issues of food insecurity and promote equitable access to healthy, sustainable food.At the heart of this farm would be the farmers themselves – a dedicated, passionate, and diverse team of individuals who havechosen to devote their lives to the stewardship of the land. They would be skilled not just in the practical aspects of farming, but also in the art of storytelling, using their intimate knowledge of the land to inspire and educate all who come into contact with it. They would be leaders in their community, advocating for policies and practices that support small-scale, sustainable agriculture, and serving as role models for the next generation of food producers.As I envision this farm, I am filled with a sense of hope and excitement for the future of our food system. In a world that is increasingly grappling with the challenges of climate change, resource depletion, and social inequality, farms like this one can serve as beacons of resilience, innovation, and community. By embracing a holistic, regenerative approach to agriculture, we can not only nourish our bodies, but also heal the land, support local economies, and foster a deeper connection between people and the natural world.It is a grand and ambitious vision, to be sure, but one that I believe is both necessary and achievable. With the right combination of passion, creativity, and collaborative effort, we can transform the way we produce, distribute, and consume food, creating a more sustainable, equitable, and vibrant future for all. And at the heart of this transformation, I see the ideal farm – a living, breathing testament to the power of human ingenuity, the resilience of nature,and the boundless potential of what we can achieve when we work in harmony with the land that sustains us.。

高考单词默写（汉英英汉乱序版）

高考单词默写（乱序版） A1. access2. accommodate3. 习惯于做某事习惯于做某事4. acknowledge5. act as6. address7. 钦佩钦佩8. admission9. adopt10. above all11. 在国内外在国内外 12. 缺席缺席13. abstract14. accompany15. 学术的学术的 16. account for17. accuse18. 考虑考虑19. acquire20. adapt21. in addition to22. 调整调整23. 被录取被录取24. adequate25. adolescent26. 利用利用27. addict28. 提前，预先提前，预先 29. accomplish30. accent31. alter32. analyze33. announce34. 周年纪念日周年纪念日35. annoy36. amateur37. 更不用说更不用说38. aggressive39. advocate40. affection41. agree with42. agreeable 43. 唱片唱片44. alert45. aid46. aim47. affair48. aircraft49. alternative50. 角度角度51. annual52. 为...担心担心 53. alcohol54. appliance55. appoint56. article57. 不妨，不如不妨，不如 58. 感到惭愧感到惭愧59. association60. astonish61. 运动员运动员62. 对...极为重视极为重视63. attempt64. 氛围氛围65. assume66. 使某人确信某事使某人确信某事 67. aspect 68. assess69. 集合集合70. assignment71. set aside72. artificial73. argue74. 合适的合适的75. approve76. arouse77. applicant78. 感激，欣赏感激，欣赏79. 如果你能，我会很感激的。

计算机专业英语

计算机专业英语----shuyingAabort vi.异常中断n.终止计划(任务) abstract adj.抽象的Access 微软公司生产的数据库软件access n..通路,访问,入门vt.存取,接近accessible adj.易接近的,可以达到的acclimate v.适应account n.计算,帐目accurate adj.正确的,精确的active adj.活动的,被激活的Active Data Objects 活动数据对象ActiveX 微软倡导的网络多媒体对象技术actual adj.实际的,真实的,现行的,目前的adapter n.适配器additional adj.另外的,附加的,额外的address n.地址vt.从事,忙于Adminstrative adj.管理的,行政的Administrator n.管理员advancement n.前进,进步advantage n.优势,有利条件advertisement n.广告,做广告advocate vt.提倡algorithm n.算法allocation n.分配,安置although conj.虽然,尽管amazing adj.令人惊奇的analog n.模拟analyze vt.分析,分解animation n.动画,活泼,有生气anticipate vt.预期,期望appeal vi.求助,要求appearance n.外观application n.应用,申请,请求appropriate adj.适当的architectural adj.建筑上的architecture n.建筑,结构archive n.档案库arithmetic n.算术arrangement n.排列,安排assembler n.装配,汇编程序assembly n.汇编,集会,大会assistance n.协助,援助,补助assistant n.助手,助教attach vt.附加,添加,系上,贴上attachment n.附件attribute n.属性,品质audio card 声卡author n.作家,创造者autocorrect v.自动更正automate v.使自动化,自动操作automation n.自动化available adj.可用到的,可利用的,有用的avoid v.避免awareness n.知道,晓得Bbasic adj.基本的basically adv.基本上,主要的basis n.基础,基本bearer n.承载人,送信人,负载的人benign adj.良性的,良好的,仁慈的betray vt.出卖,背叛,泄露,漏出……的迹象binary adj.二进制BIOS abbr.[计]基本输入输出系统Basic Input Output Systembit n.位,比特(计算机用语)bizarre adj.奇形怪状的block n.木块,石头,块breakthough n.突破brochure n.小册子browse vt.浏览budget n.预算bug n.臭虫,病菌,虫子bug-free adj.没有程序错误buggy adj.多臭虫的(程序错误的意思) bulletproof adj.防弹的bunch n.串,束v.捆成一捆bundle v.捆扎business to business(B to B,B2B)商业对商业button n.按钮Ccable n.电缆calculating speed运算速度calculator n.计算器campus n.校园capability n.能力capacitor n.电容器cassette n.盒子,盒式磁带categorize vt.加以类别,分类category n.种类caution n.警告CD-ROM n.光盘驱动器challenge n.挑战character n.字母characteristic n.特征chief adj.主要的,首要的chrominance n.色度circuit n.电路classify v.把……分类click v.单击,点击client n.顾客,客户,委托人client/server 客户/服务器clipboard n.剪贴板clock n.时钟close button关闭按钮clumsy adj.笨拙的collaborate vi.合作collision n.碰撞,冲突combat v.与…战斗,和…斗争combination n.结合,联合,合并,化合,化合物command n.命令,掌握,司令部commerce n.商业commodity n.日用品common adj.共同的,普通的commonly adv.普遍地,一般地communicate v.沟通,通信,相通communication n.传达,信息,交通,通信community n.共同体,社会compatipility n.兼容性,相容性compiler n.编译器,汇编者,编译程序compiling n.编译complex adj.复杂的component n.分量,成分,元件,组件,部件compression n.压缩comprise v.包括,构成,由……构成妥协的compote v.计算,估计,用计算机计算conceal vt.隐藏,隐蔽,隐瞒观念,概念concert n.音乐会conduct v.引导,管理,为人,传导configure vi.配置,设定confirmation n.证实,确认,批准confusion n.混乱,混淆connect v.连接connection n.连接,关系,接线connectivity n.连通性considerably adj.相当地construct vt.建造，构造，创立constantly adv.经常地，坚持不懈地consumer n.消费者contain vt.包含，容纳，容忍content n.内容contribute n.贡献control n.控件control menu 控制菜单conventional adj.常规的convert vt.转变coordinate n.同等者，同等物cord n.端口corporate adj.共同的，合作的correspond vi.符合，协调corresponding adj.相应的corruption n.腐败，贪污，堕落counter n.计算器，计数器CPU n.中央处理器crap n.废物，赌输的一注，废话crash v.崩溃critical adj.危急的，评论的，批评的cursor n.光标，游标，指针，指示器curve n.曲线，弯曲cylinder n.圆筒，圆柱体，汽缸，柱面Ddata structure数据结构database n.数据库，资料库debate v.争论，辩论debugger n.调试器，调试程序debugging n.调试decoder n.解码器dedicate vt.献（身），致力，题献dedicated adj.专用的define vt.定义，详细说明definition n.定义，解说，清晰度，精确度delegation n.代表团，授权，委托deletion n.删除，删除部分deliberately adv.故意地dependence n.依靠，依赖，信任，信赖deploy v.部署，展开，配置describe v.描述，记述desktop n.台式电脑，桌面detergent n.清洁剂detection n.察觉，发觉，探测，发现devise v.设计，策划，图谋，遗赠dial v.拨digital adj.数字的direct adj.直接的discrete adj.分离的，转折的，离散的discuss vt.讨论，论述discussion n.讨论，商议disk n.磁盘disparate adj.不同的，全异的display n.显示器v.显示disseminate v.散布distinctive adj.与众不同的，多样的distribute vt.分发，分配diverse adj.不同的，变化多样的dock v.对接document n.公文，文件，文挡，档案domain n.范围，领域DOS 磁盘操作系统download v.&n.下载drag v.拖动dramatic adj.戏剧的，剧烈的drive n.驱动器dual adj.双的，二重的，双重DVD-player n.DVD播放器dynamic adj.动态的Dynamic HTML Page Designer 动态HTML 网页设计程序Eeducational adj.教育的educe vt.得出，引出effectively adv.有效地，有利地efficient adj.效率高的electronic adj.电子的electronic commerce 电子商务Electronic Data Interchange(EDI) 电子数据交换Electronic Funds Transfer(EFT) 电子资金传送element n.要素，成分，元素elementary adj.基础的，基本的，初等的eliminate vt.排除，消除e-mail n.电子邮件emotion n.情感，感情emphasize v.强调emphatically adv.强调地，用力地employee n.职工，雇员，店员empty v.使……空enable vt.使能够encompass v.包围，环绕enhancement n.增进，增加enormous adj.巨大的enterprise n.企业，计划，事业，进去心entertainment n.娱乐entity n.实体，组合，组织，团体environment n.环境equipment n.装备，设备，器材error message 出错消息essence n.本质essential adj.本质的，实质的，基本的establish v.建立estimate v.估计，估价，评估evolve v.使……逐步形成，演化，进化evolving adj.进化的，展开的Excel 微软的表格处理软件exchange vt.交换，互换exchange ideas 交换意见executable adj.可实行的，可执行的expand v.扩展expense n.费用，开支expensive adj.昂贵的，价格高的explosive adj.爆炸性的，爆发性的extension n.延长，扩充，范围，扩展名external adj.外部的，客观的externally adv.外表上，外形上extremely adv.极端地，非常地Ffacilitate vt.使容易，使便利，促进facility n.设备，装置，工具facsimile n.传真familial adj.熟悉的，常见的favorite adj.喜爱的，喜欢的feature n.特征financial adj.财政的，金融的Flash v.闪现flexibility n.弹性，适应性，机动性flexible adj.灵活的floppy n.软驱adj.懒散的，松软的flow v.流动footprint n.足迹，脚印for instance 例如foundation n.基础，根本，建立，创立frame n.框架framework n.框架，构架，结构FrontPage 微软的制作网页工具function n.作用，功能functionality n.功能型future n.未来，将来Ggeneral adj.通用的，通常的n一般信息. generally adv.一般，通常generate vt.产生generation n.代gizmos n.小发明granular adj.粒状的group n.小组guess v.猜，猜出GUI n.[计]图形用户界面guide n.向导Hhand-help PC n.手提电脑hard disk 硬盘hardware n.硬件have a strong impact on 对……有巨大影响hesitation n.犹豫hierarchical adj.分等级的higher-quality adj.高质量的high-level language 高级语言highlighted adj.突出的high-powered adj.强有力的high-temperature adj.高温的horizontal adj.水平的host n.主机human-readable adj.易于阅读的hyperlink n.超连接hypermedia n.超媒体hypertext n.超文本II/Odevices 输入/输出设备icon n.图标idiom n.习语，方言ignore vt.不理睬，忽视imagination n.想象，想象力impact n.影响，作用improve v.改善，改进in contrast 与……对比inappropriate adj.不合适的inception n.起初inconvenient adj.不方便的，不恰当的increase n.增加，增大，增长incredible adj.难以置信的indicate v.表明individual n.个人，个体inexpensive adj.便宜的，不贵重的infect vt.传染，感染influence n.影响，感化information n.信息，消息inheritance n.遗传，遗产initial adj.最初的，词首的，初始的inkjet printer 喷墨打印机innovative adj.创新的，革新的input device 输入设备insertion n.插入install vt.安装，安置installation n.安装instruction n.说明，指令instruction set 指令系统(也作instruction system)instrument n.工具，手段，器械，器具integrate vt.结合，整合integrated adj.综合的，完整的integrated ciruit 集成电路intelligent adj.聪明的，智能的intend vt.想要，打算intensity n.亮度interactive adj.交互式的interchange vt. 交换interconnect vt. 使相互连接interconnection n. 互相联络intermediary adj. 中间的，调解的internal adj.内部的Internet n.因特网Internet Information Server(IIS)因特网信息服务器internetworking n.网络interpret v.解释，注释interpretation n.解释，阐明，口译interpreter n.解释程序，解释器，口译员interrupt v.中断intertwine v.使纠缠，使缠绕interanet 内联网introduction n.介绍invade vt.侵略，侵袭，拥挤inventive adj.善于创造的，发明的inventory n.存货，财产清册，总量invoke v.启动，调用involve vt.包括item n.项目Kkeyboard n.键盘keyword n.关键字knowledge n.知识Llanguage n.语言，语言文学，术语lapotop n.膝上型电脑large-scale 大规模的laser printer 激光打印机launch vt.使下水，发射，开办，发动，发起license n.许可，执照limitation n.局限，限制linker n.连接程序location n.地址logic adj.逻辑的logical adj.合乎逻辑的，合理的low-temperature adj.低温的luminance n.亮度Mmachine instruction 机器指令magnetic adj.磁性的magnetically adv.有磁力的，有魅力的main memory 内存mainframe n.大型机mainstream n.主流maintain v.维持maintenance n.维持，维修，坚持major adj.主要的，多的，主修的manageable adj.易处理的，便于管理的manipulate vt.操作，使用，巧妙地处理manual n.手册manually adv.用手manufacture n.制造manufacturer n.制造业者，厂商maximize/restore button 最大化/还原按钮medium n.媒体，方法，媒介Megahertz n.兆赫兹memory unit 存储单元menu bar 菜单栏mesh n.网孔，网状method n.方法microcomputer n.微型计算机microphone n.扩音器，麦克风Microsoft Transaction Server 微软事务处理服务器minimum adj.最小的，最低的mobile adj.可移动的modem n.调制解调器motherboard n.主板mouse n.鼠标MPEG addr.运动图象专家组multimedia n.多媒体multiple adj.多样的，多重的multitasking n.多任务处理muli-user adj.多用户的mutate v.变异mysterious adj.神秘的Nnative adj.本国的，本地的，与生俱来的navigation n.导航，航海，航空，领航negative n.否定，负数，底片newsletter n.时事通讯NIC abbr.网络接口卡notaion n.记法，注释，符号notebook computer 笔记本电脑note n.备注，注释notice n.注意numeric adj.数字的Oobvious adj.明显的occupy v.占用occurrence n.发生，出现，事件offer vt.提供on the lookout for 寻找，提防online n.在线operand n.操作数operate v.操作，使用operation n.操作opportunity n.机会，时机optional adj.可选择的，随意的organization n.组织original adj.原来的originator n.始发者，创造者，始发站OS (Operating System)操作系统outlet n.插座Outlook 收发邮件的软件output v.输出Ppackage n.包裹，包paperless business 无纸贸易parallel adj.平行的partner n.搭档，伙伴passive adj.被动的passive resistance 消极抵抗PCI abbr.周边元件扩展接口per prep.每，每一perform vt.履行，执行，表演peripheral adj.外围的，外围设备permission n.许可，允许permit n.通行证，许可证，执照perspective n.远景，前途PhotoDraw 图象处理软件phrase n.短语，习语picture tube 显象管pixel n.像素plug vt.堵，塞，插上pointer n.指针，指示符，指针光标polish n.光泽，优雅，精良，磨光polymorphic adj.多形的，多态的，多形态popularity n.普及，流行，声望potential adj.潜在的power supply 电源powerful adj.强大的PowerPoint 制作幻灯片和简报的软件precise adj.精确的，清晰的，严格的presentation n.表示，图象，外观，演示文稿，简报presently adj.目前，不久previous adj.以前的，早先的primitive adj.原始的，简单的，质朴的principle n.法则，原则，原理printer n.打印机priority n.优先级，优先private adj.私人的，秘密的，私有的profess n.过程，方法，作用，步骤processor n.处理器productivity n.生产力professional adj.专业的，职业的n.专家program n.程序programmable adj.可编程的programming n.编程，程序设计prompt v.&n.提示，付款期限proofread vt.校正，校对property n.财产protocol n.协议protocol suite 协议组provide v.供应，供给public key cryptography 公共密钥加密pulse n.脉冲punctuation n.标点，标点符号purchase vt.买，购买purpose n.目的，意图，用途Qqualification n.资格，条件，限制，限定queue n.队列Rrandom adj.随机的随意，任意random-access memort(RAM) 随机存储器ratio between function and price 性价比read-only memor(ROM) 只读存储器receie vt.接受recipient n.接受者recognition n.赞誉，承认，赏识，识别，重视，公认recognize v.识别，认出recommend vt.推荐rectangular adj.矩形的，成直角的reduction n.减少，下降reference n.参考refresh v.刷新regardless of adj.不管，不顾relate vt.有关联，有关系relatively adj.相对地remind vt.发布，发行remote adj.可依赖的remove vt.提醒，使想起remote adj.遥远的，偏僻的，细微的remove vt.移动represent v.代表，表明reproduce v.繁殖，复制，再生，使…..重现resident adj.居住的，长住的resolution n.清晰，分辨率resource n.资源responsible adj.有责任的，可靠的，负责的restart v.重新开始，重新启动restricted adj.受限制的，有限的resume n.履历，个人简历retrieval n.取回，修复，检索，查找retrieve v.重新回到reveal vt.展现，显示，揭示，暴露revenue n.收入，税收reverse adj.相反的revert v.恢复revolutionize v.革新riddle n.谜语robust adj.强壮的，坚定的，结实的routine n.例行公事，常规，程序runtime adj.运行时的Ssafety n.安全性scalable adj.可改变大小的，可升级的schedule n.时间表，进度表scroll v.滚动SCSI 小型计算机系统接口search n.搜寻，查究secondaries n.辅助设备section n.部分，片段，部件，地域secure v.保护，安全的，可靠的security n.安全self-replicating adj.自我复制的sequence n.顺序serious adj.严肃的setup v.&n.安装shadow n.阴影，影子，影象share vt.分享，均分，共有，分配silicon chip 硅片similar adj.类似的simplify vt.单一化，简单化simulate vt.模拟，模仿，假装，冒充simultaneously adv.同时地situation n.情况，场合SLI (Suppress Length Indicator) 控制长度指示器solt n.缝，狭槽，位置smooth adj.平滑的，正常的smoothly adv.平稳地software n.软件sophisticated adj.精制的，老练的soundboard n.声卡special functional 特殊功能的specialized adj.专门的specific adj.明确的，特殊的specification n.具体指明，规格spill vi.溢出，涌流squash v.粉碎，硬放，压坏stability n.稳定性stack n.堆栈standard adj.标准的status n.状态stereo adj.立体的stero device 音响stick v.放，置，粘住，刺，戳storage n.存储量，存储器，内存store v.存储stream n.串，流strength n.力量strive v.努力，斗争，竞争structure n.结构，构造，建筑物stuff n.原料，材料，素材，资料subnet n.子网subsume v.包容，包含subscriber n.用户端，订户，签署者suggest vt.建议，提出，暗示suite n.组supplementary adj.辅助的surfing n.网络冲浪symbol n.符号，记号，象征synonym n.同义词syntactic adj.句法的synthesis n.综合，合成system n.系统，规律，秩序，体制system unit 主机Ttailor vt.制定taskbar n.任务栏technique n.技术，技巧，方法telecommunication n.电信，无线电通讯terminal n.终端terminate v.停止，结束，终止therefore adv.因此，所以thus conj.因此timer electrical signal 定时电信号timer n.计时器tool bar 工具栏topic n.话题，主题topology n.拓扑，布局，拓扑学tour n.旅游，旅行track vt.追踪，通过traditional adj.传统的，惯例的transaction n.办理，处理，交易，事务transfer v.传输，转移，交换，转接translate v.翻译，转换，迁移，平移transformation n.变换，转换transistor n.晶体管transmission n.传输，传送，输送transmit vt.传输，传送，传达stay n.盘，碟trivial adj.琐细的，价值不高的Uundergo v.经历，经受universal adj.普遍的，全体的，世界的unpleasant adj.使人不愉快的，讨厌的unstable adj.不稳定的，不固定的，易变的upgrade vt.使升级，升级usage n.使用，用法utilize vt.利用Vvacuum tube 真空管value n.值，价值，评估，估价variation n.变更，变化，变异variety n.多样性，变化，品种，种类vast adj.巨大的，大量的version n.译文，译本，翻译vertical adj.垂直的via prep.经，通过，经由video card 显卡virtuall adv.事实上，实质上visual adj.视觉的访问者visual pollution 视觉污染volatile adj.易失的Wwealth n.财富，大量web browser 浏览器Windows 视窗操作系统wire n.电线，电报，电信workstation n.工作站wrap vt.包装，包，覆盖，隐藏Yyeah (yes) 是的。

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What future for the Distributed Systems Annex?Laurent P AUTET Samuel T ARDIEU{Laurent.Pautet,Samuel.Tardieu}@enst.fr École Nationale Supérieure des TélécommunicationsDépartement Informatique et Réseaux46,rue BarraultF-75634Paris Cedex13,FranceAbstractIn this paper,we report our experience as implementors and users of the Ada95Distributed Systems Annex(annex E of the Ada reference manual).We identify the principal strengths and weak-nesses of the annex,and make some proposals to improve it either immediately or for the next revision of the language(Ada0X).Our goal is to get an annex that is more open and compatible with other distributed systems such as CORBA,without loosing the capability of developing pure Ada rock solid distributed systems.We assume that the reader is familiar with Ada.Knowledge of the Distributed Systems Annex is useful but not required to under-stand the main ideas exposed in this article.1The Distributed Systems Annex todayA few years ago,distributed systems were mainly used by teams with very special needs in terms of processing power or reliability, or for teaching the basis of distributed programming.Today,be-cause of the dramatic growth of the Internet and the development of high speed networks,more and more people are becoming famil-iar with distributed computing.It has become quite common and well accepted to have a part of a computation done locally while the rest is being done on a server located far away.For example, the SETI@home project is dedicated toﬁnding extraterrestrial in-telligence signs in the universe.To achieve its goal,it uses a giant distributed system whose nodes are personal computers with spare CPU cycles that now look for patterns in a huge set of data collected by radio telescopes[4].The architects of Ada95[13]had foreseen this increasing inter-est in distributed systems.They chose to add a Distributed Systems Annex(DSA in short)in the latest language revision[10].This an-nex,while still fully consistent with the rest of the language,deﬁnes how subprograms can be called remotely,and how complex data structures such as pointers on remote objects and remote subpro-grams can be built and used.However,unlike foreign distributed architectures such as CORBA,those facilities preserve the strong type checking and the safety features of the Ada programming lan-guage.Permission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies arenot made or distributed for proﬁt or commercial advantage and that copiesbear this notice and the full citation on theﬁrst page.To copy otherwise,to republish,to post on servers or to redistribute to lists,requires prior speciﬁc permission and/or a fee.SIGAda’9910/99Redondo Beach,CA,USAc1999ACM1-58113-127-5/99/0010...$5.001.1Existing implementationsTwo implementations of the DSA are available at the time of writ-ing,targeting the freely available GNAT Ada compiler:1.GLADE(GNAT Library for Ada Distributed Execution),de-veloped and maintained jointly by the ENST1and by Ada Core Technologies2.This implementation is freely available under the same license as GNA T,and commercial support is available through Ada Core Technologies.It includes a par-titioning tool called gnatdist[16],and a partition communi-cation subsystem called garlic(GNAT Ada Reusable Library for Interpartition Communication)[17].2.ADEPT(Ada95Distributed Execution and PartitioningToolset)has originally started as a joint project between Com-puter Sciences Corporation3,the Texas A&M university4and the ENST.It is based on an early implementation of GLADE[11],and has since then evolved into a bridge between Adaand RMI(see section3.2).It is now maintained by the Texas A&M university.1.2Typical uses of the DSASince Ada is a general purpose programming language,distributed systems in Ada can be used potentially in every domain of com-puter science.This section describes some projects using the DSA; it is based on publicly available information available through pub-lic newsgroups and mailing lists.1.2.1IndustryGLADE has been successfully used by several major companies, both in the US and in Europe.Of course,the acceptance of the distributed features of the language is bound to the acceptance of Ada95itself,and many industrial companies are still using Ada83, even when compiling with an Ada95compiler.However,new projects and major revisions of existing products are now using Ada95and its new concepts,such as tagged types and protected types.At the same time,they do evaluate the DSA to see whether it meets their needs in terms of distributed systems.EDF,the most important electricity provider in France,has been building a prototype of a WWW session-tracker using the DSA.The goal is to keep a link between separate requests made by the same user to a WWW server.This company is also considering using the DSA as a caching proxy for database requests;if a request has already been performed in the past and if the database has not 1http://www.enst.fr/2/and http://www.act-europe.fr/3/4/been updated in the meantime,the previously computed result will be sent back to the user,thus avoiding unnecessary processing on the database server side.1.2.2MilitaryMost military projects using distributed systems written in Ada had their own communication layer,around which the whole program was designed.This has been made unnecessary with the DSA, whose goal is to let the program architect design her distributed program almost without thinking at the distribution issues.Remote subprogram calls and distributed objects integrate very well with a monolithic design.DSA could be used only as a communication layer that would replace the existing one,but the gain will be too low for such a task.It is thus often difﬁcult to fully move to the DSA without rethinking the whole program architecture.However, GLADE is starting to show up in new developments,in particular when distributed simulations are involved.Figure1:Using DSA as a communication layer For example,modern distributed interactive simulations use a standardized API called RTI(Run Time Infrastructure).This API can be called from any language,such as Ada or C++.Using RTI,one can connectﬂight simulators used by human pilots and computer-driven simulation programs,some of them written in C, others in C++and others in Ada.One implementation of RTI has been developed in Ada and uses the DSA as a communication layer [3].The DSA is hidden to the RTI programmer,who only needs to use the RTI API,but it takes care of all the communication between RTI nodes,as shown onﬁgure1.1.2.3EducationAda83has been used for years in software engineering classes, because of its high-level features such as genericity,strong-typing, encapsulation and tasking.The fact that an Ada compiler catches most errors at compile time makes it much easier for students to concentrate on the real problem rather than on a trivial mistake un-caught by a C compiler.Ada95extends the power of Ada83to object oriented and dis-tributed programming.From our own teaching experience,students enjoy using it when learning the basis of distributed programming (remote subprogram calls,distributed objects)because of its ease of use and its integration in a consistent model.For example,our students have been able to develop a complete multi-users messag-ing system based on distributed objects in a few hours.It would probably have taken much more time if they had had to cope with raw sockets and message passing.2Weaknesses of the current modelIn this section,we present the main weaknesses of the DSA in its current form.We expect that those defects will not be present in the next Ada standard;some proposals toﬁx them and to increase the capabilities of the DSA are given in section3.2.1Interoperability between Ada compilersThe design team of the DSA chose to separate the compiler from the PCS(Partition Communication Subsystem);the PCS has only a few entry points located in a standardized package called Sys-tem.RPC,and those entry points must be the only interface be-tween the code generated by the compiler and the PCS.It is thus theoretically possible to plug any PCS into any DSA-capable com-piler5.Data exchanged between the compiler and the PCS are encap-sulated into Ada streams;the PCS is not supposed to interpret their contents and must manipulate them as opaque data.This raises two major problems:1.The content of Ada streams is not normalized:for example,one compiler can choose to store an integer in a stream as it is stored in memory,while another will use another format such as XDR(eXternal Data Representation)[29].This pre-vents an Ada compiler from reading what has been stored by another,unless they agree on a common format for streams content.2.The data stored in the streams given to the PCS is unspeciﬁed.One compiler can choose,to designate a remote subprogram, to use a package name followed by a subprogram index,while another can use a package index and a subprogram index to mean the same thing.Once again,Ada compilers would have to agree on a common protocol to be able to communicate with each other.Even using a compiler from the same vendor on heterogeneous systems does not guarantee that your computers will understand each other,as the DSA does not require that heterogeneous systems be supported.2.2Interoperability with other languagesUnlike the DSA,which has been designed to write pure Ada dis-tributed programs,CORBA[22]allows parts of a distributed sys-tem to be written using different programming languages.Each part is made of one or more objects,whose interfaces are de-scribed using the Interface Description Language(IDL).A stub and a skeleton will be generated from an interface.The stub is used to perform outgoing method calls to a remote object,while the skeleton handles incoming requests and redirects them to the actual implementation of the object methods.While the skeleton is generated for the language in which the object implementation has been written,the stub can be generated for many other program-ming languages(Ada,C,C++,Java,Lisp,etc.).It is thus possible to access a remote object from programs written in another pro-gramming language,as shown onﬁgure2(the Dynamic Invocation box can be ignored and will be explained later).The multi-language characteristics of CORBA played an im-portant role in its wide acceptance:a team of developers can choose its favorite programming language to implement a service,and have another team use its own favorite language to access it.As far as interoperability is concerned,the DSA completely missed the train; the interfacing capabilities of Ada95compared to Ada83(pragma 5A validated Ada compiler does not need to be DSA capable as the DSA is an optional annex.Figure2:Global CORBA architectureImport,access to subprograms with foreign conventions)have not shown up in annex E.On the one hand,the lack of normalization of the protocol used to communicate between the partitions of a distributed Ada pro-gram forbids the development of any portable binding with remote Ada services.On the other hand,this allows distributed Ada pro-grams to avoid costly constraint checks as the strong typing is pre-served all the path along,while an interface with foreign languages would require additional checks to ensure the validity of externally acquired data.This led to a situation where people have developed two-headed distributed programs:every data exchange between two Ada par-titions is made through the DSA,while CORBA is used to export Ada services to the outside world(a concrete application can be found in[21]).However,this way of doing things is costly because two different interfaces(Ada and CORBA)need to be maintained at the same time.Also,it is error-prone,as a mismatch between the two versions may result into incorrect programs.We propose a solution to this particular problem in section3.3.Another solution commonly found to extend access to Ada re-mote objects to foreign languages is the design of small wrappers that translate a proprietary protocol into calls to the distributed ob-jects(seeﬁgure3).However,this solution has the same mainte-nance problems as the one exposed below,as two consistent inter-faces must be maintained at the sametime.NetworkMachine A Machine BFigure3:Using a proxy to access DSA services2.3Termination of a distributed applicationSince1980,we know that terminating a distributed application is not a trivial issue[8,6].To summarize the problem,an application can be globally terminated only when all the partitions are locally ready to terminate and there is no message in transit on the network that can potentially wake up one of the partitions[19].However,an Ada distributed application can be composed of a dynamic number of partitions;when using a client/server model, the number of partitions that will compose the distributed program is not known in advance.A server cannot guess whether a new client is going to connect or not.The situation is similar to the one where tasks could be created spontaneously in a non-distributed program:even if all the tasks were waiting on a select statement with a terminate alternative,should the program be terminated if a new task showed up spontaneously and tried to wake up one of those existing tasks?The reference manual does not contain anything about termi-nation of distributed applications.As a direct consequence,it does not deﬁne whether it is erroneous or not to connect a new partition to a globally ready to terminate distributed system.This particular point deserves to be speciﬁed in the reference manual.3Some proposals to extend the DSAIn this section,we propose extensions that fall in two categories: theﬁrst category contains proposals that can be adopted for the current language revision if all Ada vendor agree on their realiza-tion.The second one contains proposals to be adopted for the next Ada revision.3.1Normalization of layersThe DSA can be decomposed into three independent layers:a high-level one,in charge of the semantics of the DSA,a mid-level one,which deﬁnes the communication between compiler generated code and the PCS,and a low-level one,which represents the under-lying communication protocol.3.1.1The high-level layerThis layer contains the whole spirit of the DSA;it con-sists into the description,at the Ada language level,of what can be distributed and the semantics of every remote oper-ation.The three categorization pragmas solely dedicated to the DSA(Remote_Call_Interface,Remote_Types and Shared_Passive)open a large and consistent set of possibili-ties to distribute Ada entities,objects or subprograms.This layer has been carefully thought and leads to powerful con-structs;for example,CORBA only deals with distributed objects, while the DSA also deals with remote subprogram calls in a tradi-tional way.It also acts as a hidden naming service used to silently locate remote subprograms.However,the set of entities that can be used remotely could be slightly enlarged by introducing the notion of remote rendez-vous for example.This would require allowing a task declaration in the visible part of a Remote_Call_Interface package,as well as remote accesses to task types and objects.Of course,appropriate restrictions must be placed on types of entry parameters,just as those restrictions exist for remote subprograms.3.1.2The mid-level layerWhat we call the mid-level layer here is the declaration of the Sys-tem.RPC package.As written in section2.1,the design team of the DSA was willing to ensure a compatibility between any DSA-capable compiler and any PCS through this standardized package.While this deﬁnition allowed us to start quickly the implemen-tation of GLADE because one part of the design was implicitly contained in the annex,we soon realized that the requirement togo through System.RPC for every remote call introduces a lot of constraints.To take one example,the only non-opaque parameter given to the procedure used to do a remote subprogram call(Do_RPC)is an integer denoting the remote partition.That implies that one of the two following methods is used:1.This integer is assigned at partitioning time and the systemis closed and static(it is not easy to add new clients in a client/server architecture after theﬁrst partitioning step while the server is running,and also not easy to launch several in-stances of a single client as they will have different identi-ﬁers).2.This integer is computed at run time,and the compiler musthave a way of retrieving it by talking to the partition com-munication subsystem using another interface than Sys-tem.RPC,which defeats the capability of using the PCS with another Ada compiler.After careful thoughts,we deliberately chose to use the second method and implemented a new package named Sys-tem.Partition_Interface.This package contains all the needed subprograms to exchange localization information between generated code and the PCS.As a consequence,it is not possible for another compiler to use GLADE without generating calls to this new package.After several years of experience in maintaining GLADE,we nowﬁrmly believe that the standardization of the PCS interface is useless and should be removed from the next language revision. Moreover,it is the only case in the reference manual where some-thing that can be considered internal to the compiler has been de-scribed in an authoritative way.3.1.3The low-level layerThis part does not belong to the DSA.This is the cause of all the trouble described in sections2.1and2.2.A standardization of the communication protocol would open the road to interoperability with other systems,either written in Ada(and thus using the DSA themselves)or in foreign languages,using easy-to-use communi-cation libraries.Using a clearly deﬁned protocol does not cause any safety and efﬁciency loss,as long as the whole program is written in Ada. However,interfacing with other languages less safe than Ada may require the generation of additional checks to ensure that the ex-ternally acquired data meet Ada strong-typing constraints.Those checks could be turned on either by a pragma placed in the declara-tion of the remote package,meaning that even Ada programs would suffer a performance loss,or by a specialﬂag in each packet indi-cating whether this packet is considered safe(from an Ada point of view)or not.A proposal for such a low-level protocol is in progress,but is out of the scope of this paper.We plan to implement it for GNA T and GLADE,for compilers generating processor-speciﬁc code and for the future GNAT to JVM(Java Virtual Machine)compiler.This would,amongst other things,allow some partitions of a distributed system to run in native form(typically server partitions)while some others would run on a Java virtual machine(e.g.,client applets in a WWW browser).3.2Interfacing with RMIRMI(Remote Method Invocation)is yet another way of writing dis-tributed applications,using the Java programming language.This alternative to CORBA offers the possibility of having objects lo-cated on different hosts communicate with each other,and also lets objects with their implementation(in Java byte code)move from one host to another.This very powerful feature called code migra-tion is a big step towards the development of mobile agents.RMI is very interesting for Ada users from several point of views:Compilers that compile Ada code into Java byte code can use RMI objects and libraries to build distributed applications.A bridge between the DSA and RMI is already fully func-tional(ADEPT,see section1.1)and allows Java users to ac-cess Ada services.Sun Microsystems(author of Java and RMI)is working with the OMG(Object Management Group,the entity in charge of CORBA normalization),to use IIOP(Internet Inter-ORB Protocol)as a basis for RMI implementation,while IIOP will be extended to support the full semantics of RMI.That means that Ada code compiled into Java byte code and using RMI will be able to talk with services written with CORBA,and that the Ada/RMI bridge will be usable as a gate between the DSA and CORBA3.3Interfacing with CORBAAs written in section2.2,nothing prevents a user from maintain-ing two consistent interfaces for a service,one for the Ada side of the world using the DSA and a second for the other languages using CORBA,although this is a painful and error-prone task.In this sec-tion,we will see that other methods can be used to interface DSA and CORBA.As far as distributed objects are concerned,Ada and CORBA are close from each other.The differences and similarities between them have been studied in[27]and[24].Comparisons from a designer’s point of view have been published in[23]and [15].3.3.1Exporting DSA services to CORBAAn ongoing project is the automatic translation of DSA services into CORBA speciﬁcations so that those services can be used from a CORBA node[25].Packages categorized as Remote_Types or Remote_Call_Interface are analyzed using ASIS(Ada Se-mantic Interface Speciﬁcation)[14],and the semantic information is then utilized to generate one or more IDL modules;the imple-mentation of each module is also produced automatically.Incom-ing CORBA calls to DSA objects are automatically transformed into outgoing DSA calls.Theﬁrst version of this tool called CIAO(CORBA Interface for Ada(DSA)Objects)[26]is using exclusively the free software OmniORB2CORBA product.The gate between OmniORB2and GNAT has been developed as a separate project[1]and can be used independently.3.3.2Using a common protocolWe are currently investigating the use of IIOP as the basis of our low-level protocol,to ease the interfacing process between the DSA,CORBA and RMI.The basic idea behind this is effort split-ting:implementing a tasking runtime requires a lot of resources from Ada compilers vendors,and so does the implementation of the DSA.If some of the costs could be shared by the CORBA and RMI vendors,there would probably be more implementations of the DSA,as the existing infrastructure could be reused easily.We already have a full Ada ORB implementation[12],soon to be released as free software.This software,whose code name is Broca,will serve as a basis for both our free software CORBA product,AdaBroker,and a future version of GLADE that will be using IIOP.Using IIOP as the standard protocol for the DSA would al-low accessing CORBA and RMI services directly through the DSA without any need for an additional bridge.Also,it would be pos-sible,using an Ada to Java byte code compiler,to transfer active objects and achieve code migration in Ada using only the DSA. This would be a big step forward in terms of fault tolerance and reliability,as critical services could duplicate themselves automati-cally in order to keep for example a minimum number of instances available at any time.3.4Dynamic interfacesAnother powerful CORBA feature not found in the DSA is the abil-ity to use dynamic interfaces.Two mechanisms,DII(Dynamic In-terface Invocation,shown onﬁgure2)and DSI(Dynamic Skeleton Interface),can be used to register a class by describing its meth-ods using their names and signatures,and to build a call to those methods dynamically.The most obvious advantage is that the interface does not need to be present at compilation time.For example,a calculator ap-plication can be enriched at run time by adding new functions(as remote objects designed by their names)that are called dynami-cally as the user types names them.Explicit static calls to those functions do not appear anywhere in the calculator source code.The introduction of such a mechanism in the DSA would con-siderably ease the interfacing with CORBA,as both side could in-terface with each other using this protocol.3.5Quality of ServiceOn a completely unrelated topic,a useful extension to the exist-ing DSA speciﬁcation would be the introduction of Quality of Ser-vice(QoS)parameters.For the reader unfamiliar with this notion, a QoS speciﬁcation may be seen as a numeric value quantifying some properties of the underlying network,for example the maxi-mum delay between a request emission date and its handling on the receiver side,or a guaranteed bit rate from one partition to another.As the requests for quality of service depend heavily on the location of every service,it makes more sense to include all the QoS related information into the conﬁgurationﬁle describing the distributed application rather than in the subprogram speciﬁcation itself.To this purpose,we intend to propose the format of the gnat-dist(our partitioning tool)commandﬁle as a standard for describ-ing Ada distributed applications.Thisﬁle format willﬁrst be ex-tended to contain the necessary QoS extensions,as shown in sam-ple3.5.Sample1gnatdist extension for QoSconfiguration Demo isP1, P2 : partition;C : channel := (P1, P2);for C’Bandwidth use 1_000_000;for C’Peak use 2_000_000;for C’Max_Peak use 5.0;−− Require up to 1Mbit/s for normal execution,−− with peaks up to 2Mbits/s for a maximum of−− 5 seconds.[...]end Demo;3.5.1Network characteristicsIt is common knowledge that QoS and crude packet switching net-works do not mix well,as the transmission time of a data fragment is unrelated to the transmission time of other fragments compos-ing the same high-level packet.Unfortunately,packet switching networks are very common both in the industry and in universities (TCP/IP over Ethernet).The introduction of the new IP revision(IPv6,previously called IPng)[5]adds the notion of trafﬁc class.Thisﬁeld,present in every IPv6packet,is used by all the routers on a given path to prioritize theﬂow accordingly to a predeﬁned policy.Within an organization, it is be possible to setup all the routers to exchange data between two partitions at the highest possible priority,thus obtaining the speed and the bandwidth of the slowest physical link on the data path.However,this solution is only applicable to a company network, as the company system administrator does not control the routing and priority handling policies on external routers.The use of ATM (Asynchronous Transfer Mode)networks by Internet providers can help develop such a priority scheme between distant sites.Those networks can negotiate a guaranteed bandwidth for a complete vir-tual circuit.Once the required bandwidth has been allocated,it will never be used for something else unless the resource has been explicitly released.We have already developed a binding between Ada and ATM [18],which is being integrated in AdaSockets6,one of our free soft-ware products.The ultimate goal is to offer the ability to use ATM as the underlying networking protocol for GLADE.We are work-ing on deﬁning a syntax for the indication of the desired networking resources,that could be applied to IPv6,ATM and other protocols dealing with resource reservations such as RSVP[2].3.5.2Priority related enhancementsOne of the most needed enhancements of the DSA would be a spec-iﬁcation of how priorities in partitions of an Ada distributed pro-gram are related to each other.Right now,it is unspeciﬁed whether the priority of the caller will be used or not for executing the remote subprogram.This is even worse as the various partitions may have different scheduling policies and priority ranges,thus leading to a malfunction if priorities are propagated over the network.We have integrated new pragmas in the GLADE conﬁguration ﬁle to statically describe the behavior of incoming calls.For exam-ple,one can set an upper limit of the number of incoming remote calls that can be executing at the same time.Also,a common prior-ity map is used on all the partitions to transform the caller priority into an acceptable priority for the receiver,if the user chooses to do so(aﬂag in the conﬁgurationﬁle toggles this).This method eases the scheduling computation in a distributed application using Rate Monotonic Scheduling techniques[28].4ConclusionsWe have shown in this paper that the Distributed Systems Annex of Ada95is well deﬁned and consistent with the rest of the language, but would beneﬁt from a standardization of the protocol used to communicate between the partitions.This standardization would ease the development of Ada distributed applications using differ-ent Ada compilers,and would open the world of distributed Ada to other languages,without loosing any of the Ada safety and security.Despite those(hopefully constructive)criticisms,weﬁrmly be-lieve that the presence of the Distributed Systems Annex is a major achievement in the language deﬁnition.We want to thank again the design team who chose to make Ada even more powerful and user-friendly by including the DSA in the ISO standard.6http://www.infres.enst.fr/ANC/。