Data Flow Diagrams Quiz

Systems Analysis and Design Chapter 5: Process Modeling

• A process model graphically represents how a business system operates.
• It illustrates processes and how data moves among them.
• Data Flow Diagrams (DFDs) are a common technique to diagram business processes and the data flowing between them.
• They are a logical process model, not a physical one.
• Logical models describe processes without showing how they are performed.
• Logical models are refined into physical models which provide necessary information for building systems during the design phase.

Chapter 5 Outline

• Reading Data Flow Diagrams
• Explaining the rules and style guidelines for data flow diagrams
• Describing the process used to create data flow diagrams
• Validating data flow diagrams

Data Flow Diagram (DFD) Elements

• Process: An activity or function within the system.
  • Each should have a unique name (verb-noun).
  • Perform only one action.
  • Have at least one input and one output data flow.
  • Have a unique identification number.
• Data Flow: A single piece of data or a collection of data.
  • Represented as a noun.
  • Flows into and out of processes.
  • Show input and output data for each process.
  • Includes a description of the data elements within it.
• Data Store: A collection of data stored in the system.
  • Represented by a noun.
  • Includes a description.
  • Data flows into and out of a data store.
  • Indicates information is added to/retrieved from a data store.
• External Entity: An external person, organization, or system interacting with the system.
  • Represented by a noun.
  • Includes a description.
  • Data flow to/from a process is related to an external entity.
  • Data flows to/from an external entity relate to it.

Using Data Flow Diagrams

• Decomposition: Process breakdown into a hierarchy of DFDs for a complex system.
• Balancing: Information at one level of a DFD is reflected in the next level.
• Context Diagram: Depicts the entire system and its external environment in relation to a single system.
  • System's inputs and outputs from/to external entities.
  • No data stores within the system are present on the context diagram.
• Level 0 (or Level 0 DFD): Shows major high-level processes and their relationships within a system or process.
• Level 1 Diagram (or Level 1 DFD): Shows the internal components of a Level 0 process in more detail.
• Level 2 Diagram (or Level 2 DFD): Shows further decomposition, describing details of a level 1 DFD.

Creating Data Flow Diagrams

• Start with use case information and definitions.
• Project teams usually utilize process modeling tools.
• Use cases are rewritten as data flow diagrams.
• The project team sometimes modifies use case information to conform to data flow diagram rules in terms of names and data flows.
• Data flow diagrams are validated for accuracy and completeness. (syntax and semantic errors)

Validating Data Flow Diagrams (DFDs)

• Syntax Errors: Structure and usage of diagrams do not adhere to rules. (DFD language conventions).

• Semantic Errors: The meaning or logic of the diagram does not accurately describe the process.

• Check all data flows for: Unique name, description, connects to at least one process, shown in one direction, & minimum number of crossed lines

• Check each process for: Unique name, description, at least one input data flow, at least one output data flow, input/output data flows are different

• Check each data store for: Unique name, description, at least one input flow, at least one output flow

• Check external entities: Unique name, description, at least one input or output data flow

• Context Diagram: One context diagram for the entire system.

• Decomposition: Each process is completely described by its children.

• Balance: Data flows, stores, & entities on a higher level DFD are on the lower ones.

Holiday Travel Vehicles Example

• In the example, the information system modeled is the Holiday Travel Vehicles sales system.
• The example shows how to create a context diagram representing the system.
• Also how to proceed to creating Level 1 and Level 2 DFDs to detail processes more fully.