Data Dictionaries
A data dictionary is a file or collection of files that stores the metadata of a database. It contains details about other database objects—such as who owns the data, how the data relates to other objects, and additional descriptive information. This component is critical to any relational database. Interestingly, despite its importance, most database users never see it; typically, only database administrators interact directly with it.
Common information stored in a data dictionary includes:
- Name of the data item – The official name of the data element.
- Aliases – Alternate names for the data item. For example, DEO for Data Entry Operator or DR for Deputy Registrar.
- Description/Purpose – A short explanation of what the data item is used for or why it exists.
- Related data items – Links between data elements. For example, total_marks must always equal internal_marks plus external_marks.
- Range of values – Permitted values. For instance, total_marks must be between 0 and 100.
- Data structure definition/forms – Identifies the process names that produce or consume the data items.
If the data is primitive, it describes its physical structure.
If the data is an aggregate, it describes how it is composed of other data items.
Mathematical notations used in data dictionaries:
