Data Dictionary
Purpose
Adds details that are not typically included in DFDs, ERDs, or other documentation. There are many types of data dictionaries available and they focus on different jobs.
Terms
- Data Attribute: is the smallest piece of data that has meaning to the end-users and the business.
- Data Structures: are specific arrangements of data attributes that define the organization of a single instance data needed for a task such as a screen, report or data flow.
3 Basic Types
- Sequence – a group of data attributes that occur one after another in order.
- Selection – one or more attributes chosen from a set of attributes.
- Repetition – a group of one or more attributes that may have multiple instances within a larger data structure.
Data Structure Symbols
=: means “consists of” or “is composed of”+: means “and” and designates a sequence[...]: means only one of the attributes listed within the brackets may be present, and designates selection{...}: means the attributes within the braces may occur many times for one instance of the main data structure and designates repetition(...): means that the attribute(s) within the parentheses are optional and may not always be present
Sequence Data Structure
| Document Example | Data Structure |
|---|---|
 |
Wage And Tax Statement = Taxpayer Identification Number + Taxpayer Name + Taxpayer Address + Wages, Tips And Compensation + Federal Tax Withheld + … |
Selection Data Structure
| Document Example | Data Structure |
|---|---|
 |
Order = [Personal Customer Number, Corporate Account Number ] + Order Date + … |
Repetition Data Structure
| Document Example | Data Structure |
|---|---|
 |
Claim = Policy Number + Policyholder Name + Policyholder Address + 0{Dependent Name + Dependent’s Relationship}N + 1{Expense Description + Service Provider + Expense Amount}N |
Optional and Reusable Attributes
| Document Example | Data Structure |
|---|---|
 |
Claim = Policy Number + Policy Date = Date + Policyholder Name + Policyholder Address + (Spouse Name + Date of Birth = Date) + … Date = Month + Day + Year |
Example Creation of a Data Dictionary
- Start with an entity on an ERD.
- Document the attributes, but keep an eye for potential reuse of data structures.
- Fully break down one data structure before moving to a new entity from the ERD.
