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.