数据库工程师专业英文整理

XanaduXanadu is an overall paradigm, an ideal and general model for all computer use, based on sideways connections among documents and files. This paradigm is especially concerned with electronic publishing, but also extends to all forms of storing, presenting and working with information. It is a unifying system of order for all information, non-hierarchical and side-linking, including electronic publishing, personal work, organization of files, corporate work and groupware. All data （for instance, paragraphs of a text document） may be connected sideways and out of sequence to other data （for instance, paragraphs of another text document）。

This requires new forms of storage, and invites new forms of presentation to show these connections.On a small scale, the paradigm means a model of word processing where comments, outlines and other notes may be stored conceptually adjacent to a document, linked to it sideways.On a large scale, the paradigm means a model of publishing where anyone may quote from and publish links to any already-published document, and any reader may follow these links to and from the document.参考译文：Xanadu是一个全面的范例，是一个基于联系文档和文件的，理想的、大众化的、能为所有电脑所用的通用模型。

这个范例特别适合描述电子出版物及扩展的、所有的存储形式的信息。

他是一个针对包含电子出版物、个人工作、管理文件、团队工作和群件，等所有信息的、不分级别的链接。

所有的数据（例如，文本文档中的某一段落）中可能被链接到另外的地方或者被打乱次序发布到其它数据（例如，另外文本文档中的某一段落）中去。

这就需要新的存储形式和引入新的展现这些链接的表现方式。

从狭义上来说，这个范例中的文字处理模型中被文档链接的注释、大纲、其它的记录应该在概念上和该文档链接。

从广义上来说，这个范例中的出版模型任何人都可以引用和链接已经发行了的文档，所有的读者可以根据这些链接得到链接着的文档。

REDUCED INSTRUCTION SET COMPUTERSStudies of the execution behavior of high-level language programs hav e provided guidance in designing a new type of processor architecture：the reduced instruction set computer（RISC）．Assignment statements predominate，suggesting that the simple movement of data should be optimized．Ther e are also many IF and LOOP instructions，which suggest that the underlying sequence control mechanism needs to be optimized to permit efficient pipelining．Studies of operand refe rence patterns suggest that it should be possible to enhance performa nce by keeping a moderate number of operands in registers．These studies have motivated the key characteristics of RISC machines ：（1）a limited instruction set with a fixed format．（2）a large number of registers or the use of a compiler that optimizes r egister usage，and（3）an emphasis on optimizing the instruction pipeline．The simple instruction set of a RISC lends itself to efficient pipeli ning because there are fewer and more predictable operations performe d per instruction．[1] A RISC instruction set architecture also lends itself to the delayed branch technique，in which branch instructions are rearranged with other instructions t o improve pipeline efficiency．Although RISC systems have been defined and designed in a variety of ways by different groups，the key elements shared by most designs are these：．A large number of general-purpose registers，or the use of compiler technology to optimize register usage．A limited and simple instruction set．An emphasis on optimizing the instruction pipelineTable 2-1 compares several RISC and non-RISC systems.1．Instruction Execution CharacteristicsTo understand the line of reasoning of the RISC advocates，we begin with a brief review of instruction execution characteristics ．The aspects of computation of interest are as follows：? Operations performed：These determine the functions to be performed by the processor and its interaction with memory．? Operands used：The types of operands and the frequency of their use determine the me mory organization for storing them and the addressing modes for acces sing them．? Execution sequencing：This determines the control and pipeline organization．2．The Use of A Large Register File [2]The reason that register storage is indicated is that it is the faste st available storage device，faster than both main memory and cache．The register file is physical ly small，generally on the same chip as the ALU and control unit，and employs much shorter addresses than addresses for cache and memor y．Thus，a strategy is needed that will allow the most frequently accessed ope rands to be kept in registers and to minimize register-memory operati ons．Two basic approaches are possible，one based on software and the other on hardware．The software approac h is to rely on the compiler to maximize register usage．The compiler will attempt to allocate registers to those variables that will be u sed the most in a given time period．This approach requires the use o f sophisticated programanalysis algorithms．The hardware approach is simply to use more registers so that more variables can be held in re gisters for longer periods of time．3．Characteristics of Reduced Instruction Set ArchitecturesAlthough a variety of different approaches to reduced instruction set architecture have been taken，certain characteristics are common to all of them．These characterist ics are listed in Table 2．1 and described here．The first characteristic listed in Table 2．1 is that there is one machine instruction per machine cycle．A machine cycle is defined to be the time it takes to fetch two operands from registers，perform an ALU operation，and store the result in a register．Thus，RISC machine instructions should be no more complicated than，and execute about as fast as，microinxtructions on CISC machines．[3] With simple，one –cycle instructions，there is little or no need for microcode；the machine instructions can be hardwired[4]．Such instructions shoul d execute faster than comparable machine instructions on other machin es，since it is not necessary to access a microprogram control store duri ng instruction execution．A second characteristic is that most operations should be register-to -register，with only simple LOAD and STORE operations accessing memory．This des ign feature simplifies the instruction set and therefore the control unit．For example，a RISC instruction set may include only one or two ADD instructions （e. g. ，integer add，add with carry）；the VAX has 25&nXPath (XML Path Language)XPath is a language for selecting parts of an XML document. While XPath is a full-fledged expression language which can be used for arithmetics, string functions and other evaluations, in most cases it is regarded as a way to select parts of an XML document by selecting nodes which match certain criteria. XPath can be used as a stand-alone language, but in most cases it is embedded into host languages, the two most important host languages are XSLT and XML Schema.StatusThe older XPath 1.0 was based on an internally-defined Data Model (a subset of the XML Infoset). The newer XPath 2.0 is based on XDM, a more complex and externally defined Data Model. XPath 2.0 is much more powerful than XPath 1.0, it has a much largest set of built-in functions and supports methods for conditional processing and iterations.NetworkingStorage innovations give you improved tools to manage and share resources．The improvements to networking in Windows 2000 are equally groundbreaking．For example，you have the opportunity in Windows 2000 to remove all NetBIOS traffic from your network．The Dynamic Domain Name System（DDNS）can entirely eliminate your dependence on NetBIOS and WINS．Also，you can now build more secure Virtual Private Networks（VPNs）that leverage PK cryptography[10]．Further，support for Quality of Service （QoS）一a policy-based bandwidth management technology—is added．Some of the topics covered in this section are new in Windows 2000，others represent improvement to existing technologies.联网存储方面的创新，为你提供了用来管理和共享资源的更好手段。