数据库系统概念全套配套课件PPT ch22.ppt

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1、Chapter22:Object-BasedDatabasesChapter22:Object-BasedDatabasesComplexDataTypesandObjectOrientationStructuredDataTypesandInheritanceinSQLTableInheritanceArrayandMultisetTypesinSQLObjectIdentityandReferenceTypesinSQLImplementingO-RFeaturesPersistentProgrammingLanguagesComparisonofObject-Orientedand

2、Object-RelationalDatabasesObject-RelationalDataModelsExtendtherelationaldatamodelbyincludingobjectorientationandconstructstodealwithaddeddatatypes.Allowattributesoftuplestohavecomplextypes,includingnon-atomicvaluessuchasnestedrelations.Preserverelationalfoundations,inparticularthedeclarativeacces

3、stodata,whileextendingmodelingpower.Upwardcompatibilitywithexistingrelationallanguages.ComplexDataTypesMotivation:Permitnon-atomicdomains(atomicindivisible)Exampleofnon-atomicdomain:setofintegers,orsetoftuplesAllowsmoreintuitivemodelingforapplicationswithcomplexdataIntuitivedefinition:allowrelat

4、ionswheneverweallowatomic(scalar)values—relationswithinrelationsRetainsmathematicalfoundationofrelationalmodelViolatesfirstnormalform.ExampleofaNestedRelationExample:libraryinformationsystemEachbookhastitle,alist(array)ofauthors,Publisher,withsubfieldsnameandbranch,andasetofkeywordsNon-1NFrelatio

5、nbooks4NFDecompositionofNestedRelationSupposeforsimplicitythattitleuniquelyidentifiesabookInrealworldISBNisauniqueidentifierDecomposebooksinto4NFusingtheschemas:(title,author,position)(title,keyword)(title,pub-name,pub-branch)4NFdesignrequiresuserstoincludejoinsintheirqueries.ComplexTypesandSQLEx

6、tensionsintroducedinSQL:1999tosupportcomplextypes:CollectionandlargeobjecttypesNestedrelationsareanexampleofcollectiontypesStructuredtypesNestedrecordstructureslikecompositeattributesInheritanceObjectorientationIncludingobjectidentifiersandreferencesNotfullyimplementedinanydatabasesystemcurrently

7、ButsomefeaturesarepresentineachofthemajorcommercialdatabasesystemsReadthemanualofyourdatabasesystemtoseewhatitsupportsStructuredTypesandInheritanceinSQLStructuredtypes(a.k.a.user-definedtypes)canbedeclaredandusedinSQLc