Database EnvironmentThree Levels of AbstractionData IndependenceDescribing the DataData Manipulation LanguagesData ModelsObject-Based Data ModelsRecord-Based Data ModelsWhat Should a Database Provide?What Should a Database Provide? (cont’d)Database EnvironmentCPSC 356 DatabaseEllen WalkerHiram CollegeThree Levels of Abstraction•External level–How users perceive the data–Multiple views•Conceptual level–Description of data and relationships•Internal (Physical) level–How the data is physically storedData Independence•Logical Data Independence–External views do not change when conceptual schema changes–Existing applications do not need to be rewritten to accommodate new ones•Physical Data Independence–Conceptual schema does not change when internal schema changes (e.g. new server)Describing the Data•DDL (Data Definition Language)–Detailed definition of database schema (metadata)–Too low-level (and database-specific) for good modeling!•Object-based model (entity-relationship)•Record-based model (relational)Data Manipulation Languages•Commands to access and update databases•Procedural describes how to retrieve the data–Example: relational algebra–Analogy: Fortran•Non-procedural describes what data to retrieve–Example: SQL–Analogy: PrologData Models•Structural part–How the database is constructed•Manipulative part–What operations on data are allowed•Integrity constraints–Ensuring the data remains accurateObject-Based Data Models•Entity-Relationship•Semantic•Functional•Object-OrientedRecord-Based Data Models•Re lational•Network•HierarchicalWhat Should a Database Provide?•Ability to store, retrieve and update data•Access to metadata (e.g. names & types)•Transaction processing (all or none)•Concurrency control •Recovery from damage•Authentication & related securityWhat Should a Database Provide? (cont’d)•Support for networking & communications•Integrity assurance•Independence of programs from data•Utility services–Import, export, monitoring, usage analysis, garbage collection,