第15章 数据库应用结构与数据访问接口_2new

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1、Chapter15DatabaseInterfaceChapter15-Objectives¢Introducetothemethodsofaccessdatabaseinapplications:¢EmbeddedSQL¢DatabaseInterface¢ODBC¢OLEDBandADO¢JDBCInteractivevs.Non-InteractiveSQL¢InteractiveSQL:SQLstatementsinputfromterminal;DBMSoutputstoscreen¢Inadequateformostuses¢Itmaybenecessarytop

2、rocessthedatabeforeoutput¢Amountofdatareturnednotknowninadvance¢SQLhasverylimitedexpressivepower¢Non-interactiveSQL:SQLstatementsareincludedinanapplicationprogramwritteninahostlanguage,likeC,Java,COBOLApplicationProgram¢HostlanguageHostlanguage:Aconventionallanguage(e.g.,C,Java)thatsupplies

3、controlstructures,computationalcapabilities,interactionwithphysicaldevices¢SQL:suppliesabilitytointeractwithdatabase.¢Usingthefacilitiesofboth:theapplicationprogramcanactasanintermediarybetweentheuserataterminalandtheDBMSIntroducingSQLIntotheApplication¢SQLstatementscanbeincorporatedintoana

4、pplicationprogramintwodifferentways:¢StatementLevelInterface(SLI):ApplicationprogramisamixtureofhostlanguagestatementsandSQLstatementsanddirectives(embeddedSQL).¢CallLevelInterface(CLI):Applicationprogramiswrittenentirelyinhostlanguage¢SQLstatementsarevaluesofstringvariablesthatarepassedasa

5、rgumentstohostlanguage(library)proceduresStatementLevelInterface¢SQLstatementsanddirectives(embeddedSQL)intheapplicationhaveaspecialsyntaxthatsetsthemofffromhostlanguageconstructs¢e.g.,EXECSQLSQL_statement¢PrecompilerscansprogramandtranslatesSQLstatementsintocallstohostlanguagelibraryproced

6、uresthatcommunicatewithDBMS¢HostlanguagecompilerthencompilesprogramCallLevelInterface¢Applicationprogramwrittenentirelyinhostlanguage(noprecompiler)¢Examples:JDBC,ODBC,OLEDB,ADO,ADO.NET¢SQLstatementsarevaluesofstringvariablesconstructedatruntimeusinghostlanguage¢SimilartodynamicSQL¢Applicat

7、ionusesstringvariablesasargumentsoflibraryroutinesthatcommunicatewithDBMS¢e.g.executeQuery(“SQLquerystatement”)EmbeddedSQLEXECSQLBEGINDECLARESECTION;unsignedlongnum_enrolled;charcrs_code;charSQLSTATE[6];VariablessharedbyEXECSQLENDDECLARESECTION;hostandSQ