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SJSU CS 157A - DB Mangement Systems

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CS157A Lecture 2 DB Mangement SystemsChapter 1: Introduction1. Database TheoryPowerPoint PresentationSlide 5Slide 6Degrees of Data IndependenceLogical vs Physical Data IndependenceThree Schema ArchitectureSlide 10The External LevelSlide 12The Conceptual LevelThe Internal LevelInter-Related DataSlide 16Database Management System (DBMS)Purpose of Database SystemPurpose of Database Systems (Cont.)Levels of AbstractionView of DataInstances and SchemasData ModelsWhat is a Database Management System?Relational ModelThe DBMS MarketplaceThree Aspects to Studying DBMS'sQuery LanguagesHost LanguagesSlide 30Slide 31Slide 32Slide 33Entity-Relationship ModelEntity Relationship Model (Cont.)Slide 36A Sample Relational DatabaseData Definition Language (DDL)Data Manipulation Language (DML)SQLDatabase UsersDatabase AdministratorTransaction ManagementStorage ManagementOverall System StructureApplication ArchitecturesCS157A Lecture 2 CS157A Lecture 2 DB Mangement SystemsDB Mangement SystemsProf. Sin-Min LeeDepartment of Computer ScienceSan Jose State University©Silberschatz, Korth and Sudarshan1.2Database System ConceptsChapter 1: IntroductionChapter 1: IntroductionPurpose of Database SystemsView of DataData Models Data Definition Language Data Manipulation LanguageTransaction Management Storage ManagementDatabase AdministratorDatabase UsersOverall System Structure©Silberschatz, Korth and Sudarshan1.3Database System Concepts1. 1. Database TheoryDatabase Theory Why use database?Data is a valuable corporate resource which needs adequate, accuracy, consistency and security controls.The centralised control of data means that for many applications the data will already exist, and facilitate quicker development.Data will no longer be related by application programs, but by the structure defined in the database. Easier to maintain systems©Silberschatz, Korth and Sudarshan1.4Database System ConceptsIn the the past as new applications were written they used existing files, or created a new file for their use.Sometimes several existing files need to be sorted and merged to obtain the new file.Thus, it is probable that several files will contain the same information stored in different ways. In other words, there will be redundant and possibly inconsistent data.Consider the files for an insurance company Traditional File Systems POLICY# POLICYHOLDER PREMIUMS data ADDRESS PREMIUM-PA PREMIUM-TOTAL POLICY# POLICYHOLDER AGENCY data ADDRESS AGENT-CODE RENEWAL-DATE RENEWAL-AMT©Silberschatz, Korth and Sudarshan1.5Database System ConceptsApplications were often considered in relative isolation.Data that should have been together was not.The potential for flexible enquiry and reporting was limited.All validations were in the programs.Procedures were required to for backup and recovery.All programmers had access to all records.There was limited concurrent access. Traditional File Systems©Silberschatz, Korth and Sudarshan1.6Database System ConceptsBasic DefinitionsDatabase: A collection of related dataData: Known facts that can be recorded Schema: Some part of the real world about which data is stored in the database.Database Management System(DBMS):A software package to facilitate the creation and maintenance of a computerised database.©Silberschatz, Korth and Sudarshan1.7Database System ConceptsDegrees of Data IndependenceDegrees of Data Independence·Device Characteristics·Blocking Factors·Data Access Organisation·Physical Record Location·Logical Views (Local)·Virtual Data Items· Virtual Records·Data Value Characteristics·Data Element Name Only©Silberschatz, Korth and Sudarshan1.8Database System ConceptsLogical vs Physical Data IndependenceLogical vs Physical Data Independence GLOBALLOGICALDATABASEDESCRIPTIONApplication ProgramLocal ViewsPhysicalFilesLogical DataIndependencePhysical DataIndependence©Silberschatz, Korth and Sudarshan1.9Database System ConceptsThree Schema ArchitectureThree Schema ArchitectureANSI & ISO suggest that DBMS should have three schemas·CONCEPTUAL SCHEMA - the global logical model of the data and processing of the enterprise. i.e community user view.·EXTERNAL SCHEMA(S) - the logical application views of the CS. i.e individual user views. ·INTERNAL SCHEMA - internal level storage view.©Silberschatz, Korth and Sudarshan1.10Database System ConceptsExternal Schema 1External Schema 2External Schema nConceptualSchemaInternalSchema Three Schema ArchitectureThree Schema Architecture©Silberschatz, Korth and Sudarshan1.11Database System ConceptsThe External LevelThe External Level·Each user has a language through which they access or see the database.·For the programmer - COBOL etc, for the end-user a query language or special purpose language.·All languages will contain a data sub-language which may be tightly or loosely coupled to the host language.©Silberschatz, Korth and Sudarshan1.12Database System Concepts·DSLs generally contain a data definition language DDL and data manipulation language DML.©Silberschatz, Korth and Sudarshan1.13Database System ConceptsThe Conceptual LevelThe Conceptual Level·A representation of the entire information content of the database.·Defined with a Conceptual Schema Language which does not represent any storage or access details.·Should include all security and integrity rules and some suggest the CS should describe the total enterprise including all allowable processing.©Silberschatz, Korth and Sudarshan1.14Database System ConceptsThe Internal LevelThe Internal Level·Low level representation of entire database.·Deals with stored records rather than conceptual or external records.·Stored records may differ in structure from conceptual records and external records.·The Internal Schema is still one level away from physical records which are often called pages or blocks©Silberschatz, Korth and Sudarshan1.15Database System ConceptsInter-Related DataInter-Related DataCLAIMSRENEWALSAGENCYDBMSRENEWALSCLAIMSAGENCYQUERYData related by structureFlexible enquiry easier©Silberschatz, Korth and Sudarshan1.16Database System ConceptsMultiple ApplicationsCLAIMSAGENCYDATABASELOCALVIEWSRENEWALS©Silberschatz, Korth and Sudarshan1.17Database System ConceptsDatabase Management System (DBMS)Database Management System (DBMS)Collection of interrelated


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