Data Dictionary
Data Requirements
When designing a program, you also need to specify what data
the will need and how it will be stored.
Designing the input and output requirements of the program will usually provide
you with the majority of this information, but it needs to be presented in a
way that can be easily checked for completeness and that can be referred to
whilst the program is being written to avoid errors.
This is done by creating a data dictionary.
What is a data
dictionary?
A data dictionary is a file which contains all necessary
information and descriptions about the data that is used in the program.
Details stored include:
- Variable name/identifier
- Data type and data structure (the type and format of the data)
- Size of data
- Validation rules (used to check that the data is appropriate)
- A description of the data (what it is used for)
Data Types
- Numeric (integers and Floating point, which is a decimal number)
- Text (A-Z, a-z, 0-9)
- Boolean (Yes/No, On/Off etc.)
- Currency
Validation Rules
- Presence Check (correct data is input)
- Look-Up Check (drop down menu)
- Range Check (can be alpha numeric)
- Length Check (data is too long or short)
- Type Check (type of character input)
Relationship Types
A person name and National insurance number are related pieces
of information. This is known as a 1 to 1 (1:1) relationship as only one
national insurance number can be related to any one person.
Example:
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Table Name
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Student
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Field Name
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First name, surname, course, grades
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Data Type
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Text and Numeric
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Field Length
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1-20 characters
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Default value of field
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Default value is blank
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Field validation
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Only text input into any field
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Keys
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Relationships
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First name and surname, name and course, name and grades
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Access rights
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