软件工程第10讲

2013-7-231Noted problem①name properlyThe following should be noted that a data object is named:1)The name should fit the entire object.2)Avoid using the meaningless name.3) If hardly name a data object, you can try to decompose the DFD again.2013-7-232

Noted problem①name properlyThe following should be noted that a transformer is named1)The name should fit the entire working.2)a transitive verb + a concrete object.

3) If hardly name a transformer, you can try to decompose the DFD again.

e.g.P143Activate systemDisplay messages statusRead sensorsGenerate alarm signalOne name has only one verb 2013-7-233

Noted problem①name properly②drawing the data flow, not the control flow③first consider the stable state④neglect the trifling side issues⑤prepare redrawing at any time2013-7-234The Data Flow Hierarchy

Pab

xy

p1p2p3p4p5

abc

de

f

g

level 0

level 1

2.Level DFD2013-7-235

The top level:The middle levels:The bottom levels:depicted the boundaries of the system

depicted the division of a process, its components can be further divided.

are composed of preliminary processes-7-236

3. Top-down drawing DFD(1). Numbering①A number of subgraph is corresponding to the processing number of its fathergraph. ②A processing number of subgraph is consists of subgraph number, dot and local number.2013-7-237

Figure 5.8.4.1.2

.3

e.g.2013-7-238(2). Balancing（P128）Information flow continuity must be maintained, that is, input and output to each refinement must remain the same, this concept called balancing.2013-7-239

Figure0BAGSDEHZPT2134Figure4YEUD

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4.1

4.24.44.34.5

e.g.12013-7-2310

Figure0CBAMTNFigure2TNPQ

S

1322.1

2.2

2.3

e.g.22013-7-2311

Figure0billofladingbillofordergoodsFigure6customer

billofladingaccountnumber

quantity

126345

6.16.36.2

e.g.32013-7-2312

Considering the balancing, can neglect the twigged data flowFigure4YEUDRWPFigure0BA

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213

45

4.1

4.24.44.34.5

e.g.32013-7-2313

(3). Local data storeFig.4CAEBZHJKFig.4.3

ZXXXA

YYYALPHA

B

4.1

4.3

4.24.4

4.3.14.3.2

4.3.32013-7-2314

(4). Degree of decompositionReference principles:①Decomposition should be natural, the concepts are reasonable and distinct.

②If doesn’t affect the understandability, a DFD can be decomposed into more parts.

③Upper levels should be decomposed quickly, lower slowly.2013-7-2315

4. DFD’s improving(1)Inspecting the DFD’s correctness 1). Data conservation

Determine the competition list

Sportsman listItem Item playersSportsman list: Item players:class classname itemItem namesportsman number2013-7-2316

e.g.2Order goods bill Invoice

PriceWrite

invoice

Order goods bill: Price: Invoice:unit name goods name unit namegoods name unit price goods namegoods number amountsamounts unit pricetotal

goods number2013-7-2317

2). Data store usedFig.0Fig.4

DELTAGAMMA

4.14.3

4.214

322013-7-2318

3). Balancing between fathergraph and subgraph(2)Improving the DFD’s understandability 1). Simplifying relationship between processesThelessdataflowprocesseshave,themorerelativedependentprocessesare,soweshouldreducetheamountofdataobject(flow)betweenprocesses at best we can.2013-7-2319

e.g.Fig.0 Fig. 2

1

24

352.2

2.1

2.32.42.5

2.6

ABCJIHLKDMNEPGFJQRICMKSULHNTE2013-7-2320

e.g. process names3). Properly naming2). Even decompositionIdeally, one problem is decomposed the same size subproblems.

•Compute total effort•Write invoice•Store and print bill of lading•Process bill of order goodsandProcess•Process input•Do odd jobs