Data dictionary definition
A data dictionary is a structured collection of information about the data within a database or dataset. It acts as a reference that describes various data attributes (e.g., name, type, values, and relationships) to help those working with the data understand it better. Data dictionaries are common in database management, data analysis, and documentation.
See also: bulk data transfer
Data dictionary types
- Active data dictionaries. An active data dictionary is dynamic and integrated into the database management system (DBMS). It actively changes with the database in real time (i.e., reflects changes whenever data is added or updated). Active data dictionaries are commonly used in relational database systems like Oracle and SQL Server.
- Passive data dictionaries. A passive data dictionary is static and serves as a reference or documentation tool. It doesn’t actively change with the database — and is used as a guide for understanding data. Passive dictionaries are valuable for database administrators, developers, and analysts to understand the database structure.
Data dictionary components
- Name — The identifier of the data element or variable.
- Type — Some examples of data types are text, number, or date.
- Description — A brief explanation or definition of the data element, including its purpose and significance.
- Data length — The maximum length of the data element (for text fields) or the number of decimal places (for numeric fields).
- Data format — Specific format or pattern the data should follow (e.g., date format, currency format).
- Allowable values — The range of acceptable values for the data element, including any constraints or validation rules.
- Default value — The value that is assigned to the data element currently.
- Nullability — Indicates whether the data element can have a null or empty value.
- Source — The origin or system from which the data element is derived.
- Dependencies — Any relationships or dependencies between this data element and other data elements or tables in the database.
- Usage notes — Additional information or notes that provide context or guidance for using the data element.