Data dictionary

One of the most important parts of a database is its data dictionary. The Data dictionary is a read-only set of tables that provides information about the database. A data dictionary is a table providing a comprehensive description of each field in the database. This commonly includes: field name, data type, data format, field size, description and example. This is shown in the example below.


Field name Data type Data format Field size Description Example
UserId Number 6 Six digit number 601539
FirstName Text 20 Employee first name Jason
Surname Text 20 Employee surname Smith
DOB Date DD/MM/YYYY 10 Date of birth as a short date format 15/09/2000
HourlyPayRate Currency #####.## 8 Rate of pay in dollars per hour 24.50
Height Real #.## 3 Height in metres, with two decimal places 1.58
FeesPaid Boolean 1 Y or N for Yes or No Y


  • field name: the name of the field as it appears in the database.
  • data type: includes text, number, date, currency, yes/no (boolean).
  • data format:  any special formatting applied to the field; e.g. number of decimal places in number fields, short, medium and long date and time formats.
  • field size:  the number of characters allowed for a given field.
  • description: a simple description of field contents.
  • example: a typical field entry.

The data dictionary is structured in tables and views, just like other database data. All the data dictionary tables and views for a given database are stored in that database’s SYSTEM tablespace.

A data dictionary is an important tool for all users, from end users to application designers and database administrators.