Data Dictionaries

A data dictionary is a means for recording the metadata of some organisation (Navathe and Kerschberg, 1986). That is, data about data. Data dictionaries have been used in three ways within information systems development: 1.Conceptual data dictionaries record meta-data/process at a very high level of abstraction.2.Logical data dictionaries are used to record process and data requirements independently of how these requirements are to be met. Logical meta-data is however at a slightly lower level of abstraction than conceptual meta-data.3.Physical data dictionaries are used to record design decisions. In terms of data, physical dictionaries store details relating to actual database or file structures. The system tables at the heart of a relational DBMS are a physical data dictionary. In terms of process, physical dictionaries may store details of programs and program libraries.