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System analysis and design. Safaa s.y. dalloul. Data flow diagrams. Unit 6: Data flow diagrams. Creating Data Flow Diagrams Context Diagram Level 0 Diagram Level 1 Diagram (and Below) Validating Data Flow Diagrams. Creating Data Flow Diagrams Introduction Data Flow Diagrams (DFD)

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system analysis and design

System analysis and design

Safaa s.y. dalloul

unit 6 data flow diagrams
Unit 6: Data flow diagrams
  • Creating Data Flow Diagrams
    • Context Diagram
    • Level 0 Diagram
    • Level 1 Diagram (and Below)
    • Validating Data Flow Diagrams
  • Creating Data Flow Diagrams
    • Introduction
    • Data Flow Diagrams (DFD)
      • Reading Data Flow Diagrams
      • Elements of Data Flow Diagrams
      • Using DFD to Define Business Process
      • Process Descriptions

Creating Data flow diagrams

  • Process model describes business process-the activities that people do. Process models are developed for the as-is system and/or the to-be system.
  • Data flow diagramming, one of the most commonly used process modeling techniques.


Process model

  • A formal way of representing how a business system operates.
  • Illustrates/Explain the activities that are performed and how data moves among them.

Data flow diagramming

  • A common technique for creating process models


  • Logical process models describe processes without suggesting how they are conducted
  • Physical process models provide information that is needed to build the system

Using DFD to Define Business Process

  • Business processes are too complex to be shown on a single DFD.
  • Decomposition is the process of representing the system in a hierarchy of DFD diagrams.
  • Child diagrams show a portion of the parent diagram in greater detail.
  • Balancing involves insuring that information presented at one level of a DFD is accurately represented in the next level DFD.

Process Descriptions

  • Text-based process descriptions provide more information about the process than the DFD alone.
  • If the logic underlying the process is quite complex, more detail may be needed in the form of
    • Structured English
    • Decision trees
    • Decision tables

Context Diagrams

  • The first DFD in every business process model.
  • Context Diagram shows the entire system as context with it's environment.
  • All process models have only one context diagram.
  • Context diagram shows overall process as just one process.
  • Context Diagram shows data flows with external entities or/and any other systems in the organization.

Context Diagrams

  • In a Patient Information system in a hospital, the system will interact with three entities (Patient, Insurance company, and doctors).

Context Diagrams

  • There are many data exchanging between the system and the patient, such as:
    • Collect patient information (i.e. name, phone and address …).
    • Receive an appointment request from the patient.
    • Receive payment information from the patient
    • Deliver appointments schedule to the patient
    • Deliver bills details to the patients

Context Diagrams

  • And there are only two data flows with Insurance company:
    • Sending bills to the company
    • And receiving Payment information

Context Diagrams

  • And finally the system will produce the following reports to doctors:
    • Appointment report
    • Patient report
    • Financial reports


  • Draw the context diagram for student information system

Level 0 Diagram

  • Once you have the set of DFD fragments (One for each use case) you simply combine them into one DFD drawing that becomes Level 0 DFD.
  • In this DFD you'll add data stores.
  • Level 0 diagrams show the major process within the system, and major process within external entities, which are the sources or destination of data flows.

Level 0 Diagram

  • Try to put the first chronologically process to the left top corner, and then draw the diagram bottom right ways.
  • Reduce the number of crosses as few as possible.
  • Iteration is the cornerstone of good DFD design, the first time draw DFD to understand the system.
  • Second iteration; draw it for better understanding and to reduce number of crosses. And so on.

Level 0 Diagram

  • On Doctors office system, we have four different use cases in level 1, make appointment, maintain patient info, perform billing, and prepare management reports.
  • So you ( as analysts) have a choice to draw them all in one diagram (witch is preferred) or to divide them into four different diagrams.
  • The following is a cut of the level 0 diagram

Level 0 Diagram “Explain”

  • Patient provides his/here information (Name, and Address).
  • Process 1 checks patient's state in Patients Data Store, to update or insert …
  • Patient requests an appointment in a suitable time for him/her.
  • The process checks availability of these times by querying Appointments Data Store.

Level 0 Diagram “Explain”

  • Then Process 1 provides the patient with a potential appointments
  • So the patient will select the most suitable appointment.
  • And the Process finally updates Appointments Data Store to assign the selected appointment.
  • And finally informs the patient with this/here selection to be confirmed.

Level 1 Diagram

  • Generally, one level 1 diagram is created for every major process on the level 0 diagram.
  • Shows all the internal processes that comprise a single process on the level 0 diagram.
  • The process for creating the level 1 DFDs is to take the steps as written on the use cases and convert them into a DFD in much the same way as for the level 0.

Level 1 Diagram

  • Shows how information moves from and to each of these processes
  • If a parent process is decomposed into, for example, three child processes, these three child processes wholly and completely make up the parent process

To Explain the chart

  • This chart for a doctor office.
  • People start reading the diagrams from top-left corner of the DFD.
  • The item "Patient" is an external entity.
  • "Patient" entity has four different arrows pointing away from itself, represent bundles of data.

To Explain the chart

  • Rounded rectangles such as "Get Patient Name and Address" are actions/process that are performed.
  • Arrows are data flows, an arrow that pointing to an entity, or pointing to a process represent the inputs for this entity or process.
  • Arrows that pointing out of the entity/process represent outputsfor this entity/process.

Validating Data Flow Diagrams

  • There are two fundamentally different types of problems that can occur in DFDs, syntax errors and semantic errors.
  • Syntax Errors: refers to structure of the DFDs and whether the DFDs follow the rules of the language.
  • Semantic Errors: refers to the meaning of the DFDs and whether they accurately describe the business process being modeled.

For each DFD:

  • Check each data flow for:
    • A unique name: noun; description
    • Connects to at least one process
    • Shown in only one direction (no two-headed arrows)
    • A minimum number of crossed lines

For each DFD:

  • Check each data store for:
    • A unique name: noun; description
    • At least one input data flow
    • At least one output data flow

For each DFD:

  • Check each external entity for:
    • A unique name: noun; description
    • At least one input or output data flow

Across DFDs:

Context Diagram:

  • Every set of DFDs must have one Context Diagram


  • There is a consistent viewpoint for the entire set of DFDs

Across DFDs:


  • Every process is wholly and complete described by the processes on its children DFDs


  • Every data flow, data store, and external entity on a higher level DFD is shown on the lower level DFD that decomposes it No data stores or data flows appear on lower-lever DFDs that do not appear on their parent DFD.

Summarize the lecture

  • DFD
  • DFD Elements
  • DFD Levels
    • Context Diagram
    • Level 0
    • Level 1
    • Level 2
  • Validating DFD
safaa s y dalloul
Safaa S.y. dalloul

Thank You