This is normally represented as the data about data. It is also termed as metadata some times which gives the data about the data stored in the database. It defines each data term encountered during the analysis and design of a new system. Data elements can describe files or the processes.
Following are some major symbols used in the data dictionary :
- = equivalent to
- + and
-  either/ or
- () Optional entry
Following are some rules, which defines the construction of data dictionary entries:
- Words should be defined to understand for what they need and not the variable need by which they may be described in the program .
- Each word must be unique. We cannot have two definition of the same client.
- Aliases or synonyms are allowed when two or more enters shows the same meaning. For example a vendor number may also be called as customer number.
- A self-defining word should not be decomposed. It means that the reduction of any information in to subpart should be done only if it is really required that is it is not easy to understand directly.
Data dictionary includes information such as the number of records in file, the frequency a process will run, security factor like pass word which user must enter to get excess to the information.