Data dictionary is the centralized collection of information about data. It stores meaning and origin of data, its relationship with other data, data format for usage etc. Data dictionary has rigorous definitions of all names in order to facilitate user and software designers.
Data dictionary is often referenced as meta-data (data about data) repository. It is created along with DFD (Data Flow Diagram) model of software program and is expected to be updated whenever DFD is changed or updated.
The data is referenced via data dictionary while designing and implementing software. Data dictionary removes any chances of ambiguity. It helps keeping work of programmers and designers synchronized while using same object reference everywhere in the program.
Data dictionary provides a way of documentation for the complete database system in one place. Validation of DFD is carried out using data dictionary.
Data dictionary should contain information about the following
● Data Flow
● Data Structure
● Data Elements
● Data Stores
● Data Processing
Data Flow is described by means of DFDs as studied earlier and represented in algebraic form as described.
|[ / ]||Or|
Address = House No + (Street / Area) + City + State
Course ID = Course Number + Course Name + Course Level + Course Grades
Data elements consist of Name and descriptions of Data and Control Items, Internal or External data stores etc. with the following details:
● Primary Name
● Secondary Name (Alias)
● Use-case (How and where to use)
● Content Description (Notation etc. )
● Supplementary Information (preset values, constraints etc.)
It stores the information from where the data enters into the system and exists out of the system. The Data Store may include –
○ Internal to software.
○ External to software but on the same machine.
○ External to software and system, located on different machine.
○ Naming convention
○ Indexing property
There are two types of Data Processing:
● Logical: As user sees it
● Physical: As software sees it