PPT《DATABASE CONCEPTS》

DATABASE CONCEPTS Leo MarkCollege of ComputingGeorgia Tech(January 1999) Course Contents IntroductionDatabase TerminologyData Model OverviewDatabase ArchitectureDatabase Management System ArchitectureDatabase CapabilitiesPeople That Work With DatabasesThe Database MarketEmerging Database TechnologiesWhat You Will Be Able To Learn More About INTRODUCTION What a Database Is and Is NotModels of RealityWhy use Models?A Map Is a Model of RealityA Message to Map MakersWhen to Use a DBMS?Data ModelingProcess ModelingDatabase DesignAbstraction What a Database Is and Is Not your personal address book in a Word documenta collection of Word documentsa collection of Excel Spreadsheetsa very large flat file on which you run some statistical analysis functionsdata collected, maintained, and used in airline reservationdata used to support the launch of a space shuttle The word database is commonly used to refer to any of the following: Models of Reality REALITY structures processes DATABASE SYSTEM DATABASE DML DDL A database is a model of structures of realityThe use of a database reflect processes of realityA database system is a software system which supports the definition and use of a databaseDDL: Data Definition LanguageDML: Data Manipulation Language Why Use Models? Models can be useful when we want to examine or manage part of the real worldThe costs of using a model are often considerably lower than the costs of using or experimenting with the real world itselfExamples:airplane simulatornuclear power plant simulatorflood warning systemmodel of US economymodel of a heat reservoirmap A Map Is a Model of Reality A Message to Map Makers A model is a means of communicationUsers of a model must have a certain amount of knowledge in commonA model on emphasized selected aspectsA model is described in some languageA model can be erroneousA message to map makers: Highways are not painted red, rivers don'

t have county lines running down the middle, and you can'

t see contour lines on a mountain [Kent 78] Use a DBMS when this is important persistent storage of data centralized control of datacontrol of redundancycontrol of consistency and integritymultiple user supportsharing of datadata documentationdata independencecontrol of access and securitybackup and recovery Do not use a DBMS when the initial investment in hardware, software, and training is too highthe generality a DBMS provides is not neededthe overhead for security, concurrency control, and recovery is too highdata and applications are simple and stablereal-time requirements cannot be met by itmultiple user access is not needed Data Modeling REALITY structures processes DATABASE SYSTEM MODEL data modeling The model represents a perception of structures of realityThe data modeling process is to fix a perception of structures of reality and represent this perceptionIn the data modeling process we select aspects and we abstract Process Modeling REALITY structures processes DATABASE SYSTEM MODEL process modeling The use of the model reflects processes of realityProcesses may be represented by programs with embedded database queries and updatesProcesses may be represented by ad-hoc database queries and updates at run-time DML DML PROG Database Design is a model of structures of realitysupports queries and updates modeling processes of realityruns efficiently The purpose of database design is to create a database which Abstraction ClassificationAggregationGeneralization It is very important that the language used for data representation supports abstraction We will discuss three kinds of abstraction: Classification In a classification we form a concept in a way which allows us to decide whether or not a given phenomena is a member of the extension of the concept.