When a relational model is created, the data dictionary defines the format necessary to enter the data into the database. The data dictionary provides information on each attribute, such as its name, whether it is a key or part of a key, the type of data expected (alphanumeric, numeric, dates, and so on), and valid values. Data dictionaries can also provide information on how often the attribute should be updated, why it is needed in the database, and which business functions, applications, forms, and reports use the attribute.
Data dictionaries provide many advantages to the organization. Because they provide names and standard definitions for all attributes, they reduce the chances that the same attribute will be used in different applications but with a different name. In addition, data dictionaries enable programmers to develop programs more quickly because they don’t have to create new data names.