A data dictionary contains information about the data items in a database, including the entity or table name, attribute or field name, data type, size, whether it is required, and any validation rules. For example, a school data dictionary would specify that the Class table has attributes like ClassID which is the primary key, Classroom which is a number that must be between 1 and 10, and MainBuilding which is a yes/no field. It also describes pupil attributes like CandidateNum which is the primary key consisting of 7 numeric characters and ClassID which is a foreign key that must match an existing ClassID.
2. DATA DICTIONARY
A data dictionary is a document which contains information about the different
data items in a database.
The data dictionary should store information about the following:
• Entity name (table)
• Attribute name (field)
• Key type – (PK or FK)
• Data type – (text, number, date, Boolean etc.)
• Size – amount of space the attribute will take up
• Required – does the attribute have to contain data?
• Validation
3. DATA DICTIONARY - SCHOOL EXAMPLE
Entity Attribute Key Type Size Required Validation
Class ClassID PK Text 4 Y Length = 4
Class Classroom Number Y Range >= 1 and <=
10
Class MainBuilding Boolean Y
Pupil CandidateNum PK Text 7 Y Numeric characters
only
Pupil Forename Text 10 Y
Pupil Surname Text 15 Y
Pupil ClassID FK Text 3 Y Existing ClassID
from Class table
