資源描述：
《數(shù)據(jù)流圖與ER圖考題解析》由會(huì)員上傳分享，免費(fèi)在線閱讀，更多相關(guān)內(nèi)容在工程資料-天天文庫。
1、數(shù)據(jù)流圖與ER圖考題解析2.solutions.Drawingprinciple:Dataflowmustberelatedtoprocessing,Thereisnodataflowbetweenentitiesandentitles,storageandstorage,andnodataflowbetweenentitiesandentitles?Datastreamsthatflowintoprocessingdonothavethesamenameasthedatastreamthatflow
2、sout?(1)databalaneeprinciple?ConcealmentoflocaldatastorageWhenthedatastoredinadataflowgraphisnotthecorrespondingexternalinterfaceprocessedintheparentgraph,butonlythedatainterfacebetweencertainprocessesinthediagram,thesedataarestoredaslocaldatastorage.In
3、ordertoemphasizetheconcealmentoflocaldatastorage,ingeneral,localdatastoragecanonlybedrawnasinputsoroutputsofcertainprocesseddatainterfacesoraparticularprocess?Inaccordaneewiththetop-downmethod,adatastorageforthefirsttimewithonlyoneprocessing,thenthedata
4、storageshouldbeusedasthelocaldatastorageandprocess!ngoftheassociation,inthedatastreaminthesubgraphneednotdraw(thelayer),anddrawintheprocessingofthesubgraph,unlesstheprocessingforatomicprocessingTheprincipleofdatabalanceisdividedintotwoaspects:Accordingt
5、othehierarchicalrelationship,thedataflowgraphisgenerallydividedintothetopleveldataflowgraph,themiddledataflowgraphandthebottomdataflowgraph?Besidesthetoplayerdiagram,theremaininghierarchicaldataflowdiagramsarenumberedfrom0.Inahierarchicaldataflowdiagram
6、,theparentandchildgraphsshouldbebalanced,thatis,theinput/outputstreamofaprocessintheparentgraphmustbethesameastheinputandoutputdatastreamofitssubgraphinquantityandname?Anotheraspectofthedatabalanceissaid:eachprocessingmusthaveinputdatastreamandtheoutput
7、datastream,andaprocessingalloutputdataindatastreamcanbeobtaineddirectlyfromtheinputdataoftheprocessingflow,orthroughtheprocessingofdatagenerated.(1)afewspecificpointstopayspecialattentionto.Inadditiontotheflowofdatastorage(files)ortheflowofdatafromdatas
8、toragewithoutnaming,everyotherdatastreammusthaveanappropriatename?Theflowofdatatoafilethatrepresentsthedatathatiswrittenintoit,andthedatastreamthatflowsoutofthefilerepresentsthereadfile?Inthefulldataflowdiagram,eachfilemusthavebo
