Data Flow Diagrams
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Data Flow Diagrams
Symbols 0 D1 Data store Process External entity Information flow name
Note that the letters along the arrows in the example diagrams represent the name of the information being transferred in each direction – you should use a description of what the information is, e.g. Patient name – these names should match across the different levels of your DFD. Likewise, each process should given a name, with the number only being used in the top half of the box. There is a sample DFD fragment overleaf.
Context Diagram
The context diagram just shows the system in the context of the external entities, and what information flows in and out of the system as a whole.
X 0 EntityEntity A A Z EntityEntity B B Information Y System
The system is then subsequently broken down into its component parts – which are themselves broken down, until each process represents a single step in your system.
Level 0 DFD 1 Entity A X Entity B Entity A Process 1 Entity B
Y V Z
N 2 3 W D1 Data store N Process 2 Process 3 N
Level 1 DFD For process 2 2.1 V G Process 2.1
J
2.2 2.3 Y N H D1 Data store N Process Process N 2.2 2.3 W Level 2 DFD For process 2.2 2.2.1 H1 J1 Process 2.2.1 H 2.2.3 J Process K 2.2.3 H2 2.2.2 J2 L Process N N 2.2.2 D1 Data store N
Example DFD Fragment Appointment Possible appointments 2 Patient name Patient Patient Patient Maintain Appointmentappointment to appointments change
Patient information Available Appointment Appointment D1 Patients D2 Appointments
Decomposition Diagram
Each process in your system should be linked together in the form of a tree diagram to show how they are related, as shown below.
0 The System
1 2 3 Process 1 Process 2 Process 3
2.1 2.2 2.3 3.1 Process Process Process Process
2.1.1 2.2.1 3.2 The number of processes, and Process Process Process the names and numbers inside the boxes, should match the processes described in the main 2.1.2 2.2.2 3.3 part of the data flow diagram. Process Process Note that only the processes are Process shown – not the data stores or external entities. 2.2.3 Process 3.4 Process