1. Ch 7: using Data Flow Diagrams
CSCI 252
Ch 7: using Data Flow Diagrams

2. Data Flow Diagrams (DFD)
Analyzing data-oriented systems
Inputs
Processes
outputs
Emphasizes system logic

3. Advantages Freedom from technical commitment (neutral)
Clarify systems / subsystems (is this right?)
Communicates understanding to users (is this right?)
Analysis of systems (is anything missing?)

4. Conventions (cont)
Entity (source / destination: person, dept, machine, business)
Arrow (data flow: from->to)
Process (transforming)
Data store (examination, retrieval, addition)

5. Conventions: Basic Symbols

6. Process Naming: Inventory Control System Name reflects whole system
Inventory reporting subsystem
Name reflects whole subsystem
Verify Customer Account
Name reflects specific process

8. Context Diagram

9. Diagram 0 (parent)

11. Typical Errors Data flow arrow wrong direction
Data store to entity w/o process
Incorrect labeling
Too many processes (>9 on a sheet)
Omitting data flow
Unbalanced decomposition (diagrams don’t match)

12. Bad!

13. Good!

14. Logical vs Physical Data Flow

15. Developing Logical Flow Diagrams
Advantages
Better communication w/users
Stable systems
Understanding of business
Flexibility and maintenance
Identify redundancies

16. Transitions

20. CRUD Matrix

21. Event Response Table

22. Data Flow Diagrams

23. Data Flow Diagram

24. Data Flow Diagram

25. Use Case and Flow Diagrams

26. In class example