CPSC 471 Study Guide - Midterm Guide: Foreign Key, Data Integrity, Unique Key
17 Mar 2017
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Document Summary
Guide: data model: set of concepts -with constraints- to describe the structure of database, categories: Conceptual/entity based (high level and semantic: way many users perceive data. Physical (low level, internal: details of how data is stored in the computer. Representational (implementation: user views with some computer storage details, schemas and states, database schema: description of the structure and constraints of the database. Schema construct: components of the schema: database state: contents of the database at a moment. Valid state: satisfies the structure and constraints: distinction. Db schema changes very infrequently, but the db state changes every time db is updated. Schema: intension; state: extension: three-schema architecture, external s: Physical data model: data independence, logical: can change the conceptual schema without changing the external one and its applications, physical: can change the internal schema without changing the conceptual schema, dbms, dbms languages. Data definition language: specifies the conceptual schema, and define internal and external schemas.
