Data Dictionary

A data dictionary is a design tool

It is used to

• design the structure of a program or database
• act as a reference source during development
• be used during software maintenance and upgrade after implementation

A project's documentation can/should include multiple data dictionaries. One for each module in the program and one defining the fields for each record data type used to store an array of data (equivalent to a database table).

Data Dictionaries can be created by hand or automatically by CASE tools such as Database Design tools.

Creating a data dictionary helps understand what data is required by different parts of a program. It also helps to set out a uniform variable/field naming scheme.

Don't make validation rules overly strict, as that can lead to data degradation due to customers having to fake data for phone numbers, post-codes etc... E.g., not all countries have 8 digit phone numbers or purely numerical post-codes.

Data Dictionaries should include

• Data element name (e.g. a field's name, like "Surname")
• Short description
• Data type (character, short/integer/long, float/double, String/Text, Boolean, Date, Currency, Array, File, etc...)
• Size / Length

Data Dictionaries might include

• Null value allowed: Null or non-existing data value may or may not be allowed for an element.
• Default value: Data element may have a default value. Default value may be a variable, like current date and time of the day
• Allowed values and validation
• Whether the field is a key field (for databases)
• Rules used in calculations producing the values.
• Scope of a variable
• Data Format (e.g., for Strings, Dates, etc...)

VCE IT

• Notes on Data Dictionaries
• Slides