ITEC 1010 Lecture Notes - Lecture 3: Isam, Relational Model, Conceptual Schema
17 Nov 2017
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Document Summary
Byte (8 bits) represents a character basic building unit of data. Record a logical grouping of related fields. File a logical grouping of related records. Database a logical grouping of related files. Index lists the key fields of each record. Direct access method: data are accessed directly without the necessity to read and discard other data. Sequential access method: data are accessed the order in which the data were stored, reading everything in front, very slow, used magnetic tapes (used before) File environment: organization with various applications with multiple data, necessary to transform the data file from one format to another. A database management system can solve possible problems in the data management. Data redundancy a dbms reduces data redundancy (unnecessary data, or repeating data) Data inconsistency a dbms provides better ways for data modification. Data integrity maintains integrity of application dealing with a function. Relational data model introduced by codd (1970)
