Data Flow Diagrams (DFDs) :Data Flow Diagrams (DFDs) Mr.Prasad SawantDepartment Of Computer ScienceProf .Ramkurshana More Arts, Commerce and Science College Akurdi. Mobile :9665755707 Email:sawanprasad@gmail.comBlog:http://prasadmsawant.blogspot.com/


Data Flow Diagrams (DFDs) :Data Flow Diagrams (DFDs) Data flow diagram (DFD) is a picture of the movement of data between external entities and the processes and data stores within a system


DFD Symbols (Gane & Sarson) :DFD Symbols (Gane & Sarson) Process Data Flow Data Store Source/Sink (External Entity)


Process :Process Work or actions performed on data (inside the system) Labels should be verb phrases Receives input data and produces output


Rule 1: Process :Rule 1: Process Can have more than one outgoing data flow or more than one incoming data flow


Rule 2: Process :Rule 2: Process Can connect to any other symbol (including another process symbol)


Process: Correct/Incorrect? :Process: Correct/Incorrect?


Data Store :Data Store Is used in a DFD to represent data that the system stores Labels should be noun phrases


Rule: Data Store :Rule: Data Store Must have at least one incoming and one outgoing data flow


Source/Sink (External Entity) :Source/Sink (External Entity) External entity that is origin or destination of data (outside the system) Is the singular form of a department, outside organisation, other IS, or person Labels should be noun phrases Source – Entity that supplies data to the system Sink – Entity that receives data from the system


Rule: Source/Sink :Rule: Source/Sink Must be connected to a process by a data flow


Rules for Using DFD Symbols :Rules for Using DFD Symbols Data Flow That Connects YES NO


Context Diagram :Context Diagram Top-level view of IS Shows the system boundaries, external entities that interact with the system, and major information flows between entities and the system. Example: Order system that a company uses to enter orders and apply payments against a customer’s balance


Level-0 DFD :Level-0 DFD Shows the system’s major processes, data flows, and data stores at a high level of abstraction When the Context Diagram is expanded into DFD level-0, all the connections that flow into and out of process 0 needs to be retained.


Lower-Level Diagrams :Lower-Level Diagrams Functional Decomposition An iterative process of breaking a system description down into finer and finer detail Uses a series of increasingly detailed DFDs to describe an IS Balancing The conservation of inputs and outputs to a data flow process when that process is decomposed to a lower level Ensures that the input and output data flows of the parent DFD are maintained on the child DFD


Strategies for Developing DFDs :Strategies for Developing DFDs Top-down strategy Create the high-level diagrams (Context Diagram), then low-level diagrams (Level-0 diagram), and so on Bottom-up strategy Create the low-level diagrams, then higher-level diagrams


Slide 17:Exercise: Precision Tools sells a line of high-quality woodworking tools. When customers place orders on the company’s Web site, the system checks to see if the items are in stock, issues a status message to the customer, and generates a shipping order to the warehouse, which fills the order. When the order is shipped, the customer is billed. The system also produces various reports. Draw a context diagram for the order system Draw DFD diagram 0 for the order system


Identify Entities,Process,Data Stores & Data Flow :Identify Entities,Process,Data Stores & Data Flow Entities Customer Warehouse Accounting Processes 1.0 Check Status 2.0 Issue Status Messages 3.0 Generate Shipping Order 4.0 Manage Accounts Receivable 5.0 Produce Reports Data Stores D1 Pending Orders D2 Accounts Receivable Data Flows Order In-Stock Request Order Data Status Data Status Message Shipping Order Order Data Invoice Shipping Confirmation Payment Accounting Data Accounts Receivable Data Order Data Inventory Reports 1.0 2.0 3.0 4.0 5.0


Slide 19:Context Diagram of Order System


Slide 20:Level-0 of Order System