A data dictionary is a set of metadata that contains definitions and representations of data elements.

Within the context of a DBMS, a data dictionary is a read-only set of tables and views. The data dictionary is a database in its own right. Amongst other things, a data dictionary holds the following information:

• Precise definition of data elements

• Usernames, roles and privileges

• Schema objects

• Integrity constraints

• Stored procedures and triggers

• General database structure

• Audit information

• Space allocations

One benefit of a well-prepared data dictionary is a consistency between data items across different tables. For example, several tables may hold telephone numbers; using a data dictionary the format of this telephone number field will be consistent.

When an organization builds an enterprise-wide data dictionary, it may include both semantics and representational definitions for data elements. The semantic components focus on creating precise meaning of data elements. Representation definitions include how data elements are stored in a computer structure such as an integer, string or date format. Data dictionaries are one step along a pathway of creating precise semantic definitions for an organization.

Initially, data dictionaries are sometimes simply a collection of database columns and the definitions of what the meaning and types the columns contain. Data dictionaries are more precise than glossaries (terms and definitions) because they frequently have one or more representations of how data is structured. Data dictionaries are usually separate from data models since data models usually include complex relationships between data elements.

Data dictionaries can evolve into full ontologies when discrete logic has been added to data element definitions.

See also

• ISO-11179
• Data element
• Data model
• Web Ontology Language
• Semantic spectrum

ISO-11179 (formally known as the ISO/IEC 11179 Metadata Registry Standard) is a standard for representing Metadata for an organization in a Metadata Registry. ... In metadata, the term data element is an atomic unit of data that has: an identification such as a Data element name a clear Data element definition one or more Representation terms optional enumerated values In telecommunication, the term data element has the following components: A named unit of data... A data model is a model that describes in an abstract way how data is represented in a business organization, an information system or a database management system. ... OWL is an acronym for Web Ontology Language, a markup language for publishing and sharing data using ontologies on the Internet. ... The semantic spectrum describes a series of technologies for creating increasingly precise definitions for data. ...

External links

• http://e-docs.bea.com/wlp/docs81/db/4Schemas.html#1062486
• Term definition from Webopedia
• Term definition from Google
• http://www.sims.monash.edu.au/subjects/ims1001/assets/week9!200501.ppt
• http://hsc.csu.edu.au/ipt/info_systems/2-4/database_modelling.htm#creating