1. SDLC Phase III: Structuring System Requirements
Dr. Dania Bilal
Spring 2009

2. SDLC Phase III Structuring system requirements
Data Flow Diagrams (DFDs)
Analysis tool to structure user requirements in a system
Graphically represents data movement or flow in an information system and relationships among data flow

3. DFDs Show the processes that transform or change data
Focus on movement of data between processes
DFDs are called process models
Process modeling shows data flow through the system based on an organization’s rules, decisions, and policies

4. DFDs Increase software development productivity by
avoiding mistakes in representing user requirements
Saves money in software cost
Based on user requirements gathered in previous phase
Evolves from the more general to the more specific

5. DFDs DFDs of current system DFDs of new logical system
Used to understand current system
DFDs of new logical system
Used to show data flow, structure, and functional requirements of new system

6. DFD Symbols Flow of data is represented by Data flow Data Store
Process
Source (external entities)

7. DFD Symbols: Data Flow
Data in motion from one place in a system to another
Example: Querying a database
Students: Describe how this activity flows from an interface by a user?
Give another example.

8. DFD Symbols: Data Store
Physical location or various locations of data in an information system
Example:
A data store in a circulation system contains data about
Students
Faculty and staff
Community and other users

9. DFDs Symbols: Process Actions performed on data for
Transformation
Storage
Distribution
Data may be represented in
File folder
Notebook
Tables
Other formats

10. DFD Symbols: Source/Sink
Depicts the origin and/or destination of data
Refers to a external entity
Another organization or unit that sends and receives information from the system
A person who interacts with the system, inside or outside
Another information system that exchanges information with the system under analysis

11. DFD Symbols: Source/Sink
Defines the system boundaries
Data originates outside a system from one or more sources
System produces information to one or more sinks

12. DFD Mechanics How the four symbols are represented?
Data flow: drawn as an arrow
Data store: drawn as a rectangular
Process: drawn as a circle
Source/sink: drawn as a square

13. DFD Definitions Level - 0 diagram Context diagram Level N diagram
Represents a system’s major processes, data flow, and data stores at the highest level of detail
Context diagram
Shows major flow between entities and the system (too general)
Level N diagram
A DFD that results from a decomposed Level-0 diagram

14. Types of DFD Current logical New logical Depicts current system
Has additional functions
Inefficient data flows are reorganized

15. DFDs New physical Examples
Depicts physical implementation of the new system
Examples
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