A data dictionary, also known as a metadata dictionary or data catalog, is a critical component of data management and database documentation. It serves as a centralized repository of information about data elements (such as tables, columns, data types, constraints, and relationships) within a database or data system. The primary purpose of a data dictionary is to provide a clear and comprehensive reference for understanding and managing data assets. Here’s what a data dictionary typically includes:

Table and Column Descriptions:

  • Names and descriptions of tables, including their purpose and usage.
  • Names, descriptions, and data types of columns within each table.
  • Indications of whether columns are nullable or have constraints (e.g., primary keys, unique keys, foreign keys).

Data Types and Lengths:

  • Definitions of data types used in the database (e.g., INTEGER, VARCHAR, DATE) and their maximum lengths.


  • Definitions of constraints applied to columns, including primary keys, unique keys, foreign keys, check constraints, and default values.


  • Information about relationships between tables, specifying which columns serve as foreign keys and link to primary keys in other tables.

Indexes and Performance Information:

  • Details on indexes created to improve query performance.
  • Notes on the intended use and benefits of each index.

Stored Procedures and Functions:

  • Descriptions of stored procedures and functions, including their names, parameters, and purposes.
  • Input and output data types for procedures and functions.


  • Definitions of views, including the underlying SQL queries and their purposes.
  • Information on which tables or columns are included in each view.

Data Validation Rules:

  • Rules and logic used for data validation and data integrity.
  • Information on how data is validated before insertion or updating.

Historical Data and Versioning:

  • Details on how historical data is managed, if applicable (e.g., using timestamps or versioning).

Authorship and Ownership: – Information about who created and owns the database objects, procedures, and views. – Contact information for individuals responsible for maintaining the data.

Usage and Access Information: – Information about who has access to the data and the purpose of access (e.g., reporting, analytics, application usage).

Data Security: – Data security measures and access controls in place to protect sensitive information.

Glossary of Terms: – Definitions of common data-related terms and abbreviations used within the database.

Change History: – Records of changes made to the database schema, including dates, reasons for changes, and responsible parties.

Documentation Standards: – Guidelines and standards for documenting the database and data elements.

A well-maintained data dictionary provides valuable insights for data professionals, database administrators, developers, and other stakeholders. It enhances data understanding, promotes data consistency, aids in troubleshooting, supports compliance efforts, and facilitates collaboration within an organization’s data management efforts.

A Sample Data dictionary using MS Excel you can download from below link.

By Abhishek K.

Author is a Architect by profession. This blog is to share his experience and give back to the community what he learned throughout his career.