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Data Flow Diagram

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Data Flow Diagram

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Data Flow Diagram

  1. 1. System Analysis & DesignSystem Analysis & Design
  2. 2.  Where do they fit in?  Analysis (What do we do?)  Fact finding  investigate business process and the current system  modelling the current and required systems  deliverables -  requirements specification  logical models of the required system  Life Cycle Phases  Planning  Feasibility Study  Analysis  Design  Code and Unit test
  3. 3.  3  DFDs describe the flow of data or information into and out of a system  what does the system do to the data?  A DFD is a graphic representation of the flow of data or information through a system Data Flow Diagrams (DFD)
  4. 4.   external entity - people or organisations that send data into the system or receive data from the system  process - models what happens to the data i.e. transforms incoming data into outgoing data  data store - represents permanent data that is used by the system  data flow - models the actual flow of the data between the other elements 4 Main Elements
  5. 5.  Notation Process box D Data Store External Entity Data Flow • Data Flow • Process • External Entity • Data Store
  6. 6.  DFD Shapes from Version F r o m F lo w C h a r t / D a t a F lo w D ia g r a m P r o c e s s D a t a S t o r e E x t e r n a l E n t it y F r o m S o f t w a r e D ia g r a m / G a n e - S a r s o n D F D P r o c e s s ID # ID # E x t e r n a l E n t it y D a t a S t o r e1 External Entity Data Store Process From Flow Chart / Data Flow Diagram Version 5.x Version 2000
  7. 7.  4  Even a small system could have many processes and data flows and DFD could be large and messy  use levelled DFDs - view system at different levels of detail  one overview and many progressively greater detailed views Levelled DFDs
  8. 8.   models system as one process box which represents scope of the system  identifies external entities and related inputs and outputs  Additional notation - system box Level 0 - Context Diagram System boxExternal entity Data flow out Data flow in
  9. 9.   gives overview of full system  identifies major processes and data flows between them  identifies data stores that are used by the major processes  boundary of level 1 is the context diagram Level 1 - overview diagram
  10. 10.   level 1 process is expanded into more detail  each process in level 1 is decomposed to show its constituent processes  boundary of level 2 is the level 1 process Level 2 - detailed diagram
  11. 11.  Duplicates marked by diagonal line in corner  System Boundary  Elementary Processes - star in corner  Process that is levelled - dots on top Other Notation
  12. 12.  5  Numbering  Labelling  Balancing Rules for DFDs
  13. 13.   On level 1 processes are numbered 1,2,3…  On level 2 processes are numbered x.1, x.2, x.3… where x is the number of the parent level 1 process  Number is used to uniquely identify process not to represent any order of processing  Data store numbers usually D1, D2, D3... Numbering
  14. 14.   Process label - short description of what the process does, e.G. Price order  Data flow label - noun representing the data flowing through it e.G. Customer payment  Data store label - describes the type of data stored  Make labels as meaningful as possible Labelling
  15. 15.   Balancing  any data flows entering or leaving a parent level must by equivalent to those on the child level  Data stores  data stores that are local to a process need not be included until the process is expanded Balancing and data stores
  16. 16.   Allowed to combine several data flows from lower level diagrams at a higher level under one data flow to reduce clutter  Flows should be labelled except when data to or from a data store consists of all items in the data store Data Flows
  17. 17.   Find the people who send data into the system  Often data is part of a PHYSICAL transaction  When handing a bar of chocolate to a shopkeeper, you are handing him/her a barcode.  Find the people who get data out of the system.  The only data you need is data that is transformed or sent completely out of the system – not data that is handled by an operator within the system. Context Diagram
  18. 18. Design Strategy Context Diagram
  19. 19. Design Strategy DFD
  20. 20. Design Strategy DFD
  21. 21. Design Strategy DFD
  22. 22. Design Strategy DFD
  23. 23.  Font: Arial Font Size: 12 Title Page Margin Top: 2” Bottom: 1” Left: 1.5” Right: 1” SAD Documentation Font: Arial Font Size: 12 Page Margin Top: 1” Bottom: 1” Left: 1.5” Right: 1”

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