Procedure for Preparing Data Flow Diagram
The procedure for producing a data flow diagram • Identify and list external entities providing inputs/receiving outputs from system; • Identify and list inputs from/outputs to external entities; • Draw a context DFD
Defines the scope and boundary for the system and project
1. Think of the system as a container (black box) 2. Ignore the inner workings of the container 3. Ask end-users for the events the system must respond to 4. For each event, ask end-users what responses must be produced by the system 5. Identify any external data stores 6. Draw the context diagram i. Use only one process ii. Only show those data flows that represent the main objective or most common inputs/outputs • identify the business functions included within the system boundary; • identify the data connections between business functions; • confirm through personal contact sent data is received and vice-versa; • trace and record what happens to each of the data flows entering the system (data movement, data storage, data transformation/processing) • Draw an overview DFD - Shows the major subsystems and how they interact with one another - Exploding processes should add detail while retaining the essence of the details from the more general diagram - Consolidate all data stores into a composite data store • Draw middle-level DFDs - Explode the composite processes • Draw primitive-level DFDs - Detail the primitive processes - Must show all appropriate primitive data stores and data flows • verify all data flows have a source and destination; • verify data coming out of a data store goes in; • review with "informed"; • explode and repeat above steps as needed.
Balancing DFDs
• Balancing: child diagrams must maintain a balance in data content with their parent processes • Can be achieved by
Defines the scope and boundary for the system and project
1. Think of the system as a container (black box) 2. Ignore the inner workings of the container 3. Ask end-users for the events the system must respond to 4. For each event, ask end-users what responses must be produced by the system 5. Identify any external data stores 6. Draw the context diagram i. Use only one process ii. Only show those data flows that represent the main objective or most common inputs/outputs • identify the business functions included within the system boundary; • identify the data connections between business functions; • confirm through personal contact sent data is received and vice-versa; • trace and record what happens to each of the data flows entering the system (data movement, data storage, data transformation/processing) • Draw an overview DFD - Shows the major subsystems and how they interact with one another - Exploding processes should add detail while retaining the essence of the details from the more general diagram - Consolidate all data stores into a composite data store • Draw middle-level DFDs - Explode the composite processes • Draw primitive-level DFDs - Detail the primitive processes - Must show all appropriate primitive data stores and data flows • verify all data flows have a source and destination; • verify data coming out of a data store goes in; • review with "informed"; • explode and repeat above steps as needed.
Balancing DFDs
• Balancing: child diagrams must maintain a balance in data content with their parent processes • Can be achieved by