ISYS224 Lecture Notes - Lecture 1: Conceptual Schema, Referential Integrity, Conceptual Model
Document Summary
Each program defines and manages its own data. Each program maintains its own set of data - users disadvantaged. Data dependence- file structure defined in program code. Duplication of data- same data held by different programs, wasted space, data/format inconsistency. Database, a shared collection of logically related data and a description of this data. Provides description of data to enable program data independence. Comprises entities, attributes and relationships or organizations information. Software system enables users to define, create, maintain and control access to the database. Computer program that interacts with database by issuing appropriate requestion (sql statement) to dbms) Permits specification of data types, structures and any data constraints. General enquiry facility (query language) of the data. Users can have their own view of db. Mechanism to customize the appearance of the database. Present consistent, unchanging picture of the structure of the database. Procedures: instructions and rules for design and use of database and dbms.