131.4 Designing a data dictionary

Learn how to describe the variables used in a program using a structured table called a data dictionary.

What is a data dictionary?

A data dictionary is a structured table that defines the variables used in a software system. It is beneficial during planning and documentation, and supports debugging, collaboration, and security auditing.

Each row in the dictionary describes a variable’s

• Name

• Data type

• Format for display

• Storage size

• Description

• Example value

• Validation rules

Example data dictionary

Variable name	Data type	Format	Size	Description	Example	Validation
username	String	A-Z, a-z	15	User's login name	jlee01	6–15 characters
dob	Date	YYYY-MM-DD	10	Date of birth	2008-06-25	Must be before today
score	Integer	###	3	Player's current score	157	Between 0 and 999
is_active	Boolean	TRUE/FALSE	1	Whether account is active	TRUE	Must be TRUE or FALSE

How to use a data dictionary

• During planning Use it to define what data your program needs.

• During coding Refer to it to avoid mistakes and inconsistencies.

• During debugging Helps check for type mismatches or invalid data.

• During teamwork Ensures all team members understand the variables.

Data dictionaries and security

Using a data dictionary improves secure coding by:

• Preventing the use of unsafe or undocumented variables

• Allowing for validation rules to be documented and enforced

• Supporting clear variable naming that avoids shadowing or reuse

• Making input/output expectations explicit for each variable

This aligns with defensive coding practices and is a foundation for secure input handling.

Key concepts

• A data dictionary describes variables in a software system.

• It supports clarity, maintenance, and debugging.

• Format, size, and validation are important for security and correctness.

• It is a useful planning tool and documentation aid.

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Linked content: Secure programming practices (410.2)

The way you name, define, and validate variables directly affects how secure your software is. In 410.2 Secure programming practices, you’ll explore how constants, data types, and input validation techniques reduce vulnerabilities such as input injection and data corruption. The principles you’re learning here in 131 lay the groundwork for secure coding later in the course.