What can dataflow diagrams be used to catalog?
Data processes Flows Stores Structures Elements
Data dictionary
- A reference work of data about data (metadata)
- Collects and coordinates data terms, and confirms what each term means to
different people in the organisation - The bridge between processes and data structures/stores
What is the need for understanding the data dictionary?
- Provide documentation
- Eliminate redundancy
- Validate data flow diagram
- Provide a starting point for developing screens and reports
- Determine the contents of data stored in files
- Develop logic for DFD processes
Data repository
large collection of project information
What does the data repository include?
- Information about data maintained by the system
- Procedural logic and use cases
- Screen and report design
- Data relationships
- Project requirements and final system deliverables
- Project management information
Data dictionary categories
Data flows
Data structures
Elements
Data stores
Algebraic notation used to describe data structures
=
is composed of
+
and
{ }
repetitive elements
[ ]
either/or situation
( )
optional element
Structural records
- Structure may consist of elements or structural records
Group of elements such as:
o Customer name
o Address
o Telephone - Each element is further defined until it is broken down into component elements
what does the notation mean?
{ C }
C is repeating but is optional
what does the notation mean?
[ C | D | E]
There is an option to choose C, D or E
Logical data structures
Show what data the business needs for its day to day operations
Physical data structures
Includes additional elements necessary for implementing the system
Features of physical data structures
- Key fields used to locate records
- Codes to identify record status
- Transaction codes to identify different record types
- Repeating group entities
- Limits on items in a repeating group
- Password
Data element characteristics
- Element ID
- Name of element
- Aliases
- Short description
- Element is base or derived - - Element length
- Type of data
- Validation criteria
- Default value
Element ID
- Optional Entry
- Allows analyst to build automated data dictionary entries
Base Element
Initially keyed into the system
Derived Element
Created by a process, usually as the result of a calculation
Types of data
and formats
Alphanumeric or text Formats: o Mainframe: packed, binary, display o Microcomputer (PC) formats o PC formats like currency, number
Creating the data dictionary
- Entries are created after data flow diagram is completed or as data flow diagram is being developed
- Created using top down approach
o Structure
o Elements
o Break down elements
Developing data stores
- Represent data at rest
- Contain information of a permanent or semi permanent nature
- “User views” If data stores are created for only one report or screen
