Definition
A data dictionary is a centralized repository that contains definitions and details about the data within a database or dataset.
It serves as a reference guide for understanding data elements and their relationships. Data dictionaries are common in data analysis, database management, and documentation.
Data Dictionary Types
- Active data dictionaries: This is dynamic and incorporated within the database management system (DBMS). They actively update the database, reflecting changes as new data is added or modified. Active data dictionaries are common in relational database systems such as SQL servers and Oracle.
- Passive data dictionaries: These are static and act as a documentation tool or reference. They don’t update the database but serve as a guide for understanding data. Database administrators, developers, and analysts use them to understand the database structure.
Data Dictionary Components
- Name: Identifies the data element or variable.
- Type: Data types include text, number, or date.
- Description: Explains or defines the data element, including its significance and purpose.
- Data length: Indicates the maximum allowable length for text fields or the precision for numeric fields.
- Data format: Shows the precise format or pattern the data should follow.
- Allowable values: Specifies the acceptable range of values for the data element, including validation rules or constraints.
- Default value: The currently assigned value for the data element.
- Nullability: This shows if the data element can have an empty or null value.
- Source: The origin or system from which the data element is derived.
- Dependencies: Specify any dependencies or relationships between data elements and other data elements in the database.
- Usage notes: Additional notes or information that offer context or guidance for using the data element.