A data dictionary, data repository, or information repository, is a special repository that describes the data that is contained within a database. This data can include information about the database’s schemas and constraints, user information, program descriptions, usage standards, and design decisions (Elmasri & Navathe, 2015). The extent of a data dictionary can vary depending on the needs and specifications of a particular application. However, it should generally contain a comprehensive listing of data object names and definitions; properties of each data element; diagrams describing the database, such as entity-relationship diagrams. A data dictionary can also contain instructions for reading and using the data. For instance, the format of alphanumerical codes, units of measurement used, and rules for treating null or empty fields can be included if necessary.
Data dictionaries are a powerful tool for documentation and communication. A data repository can help standardize data, particularly if it is received from multiple sources or accessed by multiple users. Furthermore, the comprehensive documentation contained within a data dictionary facilitates design processes related to the collection or use of the data, or when the database needs to be modified. The precise descriptions of data entities and the relationships are a valuable resource for designing applications that use the data. If multiple applications make use of the same data, a reliable data dictionary can supply all of their documentation needs. Finally, an information repository ensures that the meaning of each element in a database is preserved across users, sources, and implementations. These benefits become increasingly relevant as the size and complexity of the database grow, and more users become involved in its creation, maintenance, and use. As such, creating a data repository is a critical part of database design, especially in large corporate or scientific use.
Reference
Elmasri, R., & Navathe, S. B. (2015). Fundamentals of Database Systems (7th ed.). Pearson.