Data Flow Diagrams Objectives:

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Presentation transcript:

Data Flow Diagrams Objectives: To define what is meant by structured analysis To define the symbols used in a Data Flow Diagram (DFD) To draw a context diagram (Level 0 DFD) for a given scenario To refine a DFD to a more detailed (lower-level) view

Structured analysis A widely-used top-down method for defining system inputs, processes and outputs. It shows how information flows through a system, using several diagrams showing progressively more and more detail at each level. The primary tool of structured analysis is the Data Flow Diagram (DFD).

Data Flow Diagrams The following four symbols are used in data flow diagrams: External entity Process Data store Data flow

Data flow diagram of a travel agent booking system Customer Travel-query Available flights Book flight flights Booking Booking confirmation

Data flow diagram of part of an order processing system Customer Order Available stock stock Process order Invoice Unfilled order Out-of-stock notice backorders Despatch note Warehouse

Order rejection notice Context diagrams a top-level DFD shows the least amount of detail and is known as a Level 0 DFD or context diagram. Order Customer Invoice Warehouse Picking List Process order Out-of-stock notice Order rejection notice

Level 0 or context diagram shows a system as a single process with inputs and outputs flowing to or from external entities. Level 1 DFD will split up that single process into subsystems and show more detail about the data flows and data stores. Level 2 DFD may decompose a single subsystem even further.