Ch 7: using Data Flow Diagrams CSCI 252 Ch 7: using Data Flow Diagrams
Data Flow Diagrams (DFD) Analyzing data-oriented systems Inputs Processes outputs Emphasizes system logic
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?)
Conventions (cont) Entity (source / destination: person, dept, machine, business) Arrow (data flow: from->to) Process (transforming) Data store (examination, retrieval, addition)
Conventions: Basic Symbols
Process Naming: Inventory Control System Name reflects whole system Inventory reporting subsystem Name reflects whole subsystem Verify Customer Account Name reflects specific process
Context Diagram
Diagram 0 (parent)
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)
Bad!
Good!
Logical vs Physical Data Flow
Developing Logical Flow Diagrams Advantages Better communication w/users Stable systems Understanding of business Flexibility and maintenance Identify redundancies
Transitions
CRUD Matrix
Event Response Table
Data Flow Diagrams
Data Flow Diagram
Data Flow Diagram
Use Case and Flow Diagrams
In class example