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06 Data Flow Diagrams - Exploding

And Franchise Colleges. 06 Data Flow Diagrams - Exploding. By MANSHA NAWAZ. Learning Aims. Aim to be able to explode a process on a top-level DFD Objectives to distinguish primitive/non primitive processes to identify appropriate sub-processes to identify local data stores

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06 Data Flow Diagrams - Exploding

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  1. And Franchise Colleges 06 Data Flow Diagrams - Exploding • By MANSHA NAWAZ DFD - Exploding

  2. Learning Aims • Aim • to be able to explode a process on a top-level DFD • Objectives • to distinguish primitive/non primitive processes • to identify appropriate sub-processes • to identify local data stores • to construct the exploded DFD consistent with the parent DFD DFD - Exploding

  3. Lecture Outline • selecting processes for exploding • initial inputs and outputs • identifying sub-processes • local data stores • diagram construction • consistency checking • diagram hierarchy DFD - Exploding

  4. Checking Processes on the DFD • check each process, can it be broken down into meaningful sub-processes? • no • a functional primitive • do not explode • yes • explode the process Q 3 enter order 1 check stock þ DFD - Exploding

  5. Inputs & Outputs to Explosions • each exploded process has its own inputs and outputs • the data flows into the process must all appear as inputs to the exploded process • the data flows out of the process must all appear as outputs from the exploded process DFD - Exploding

  6. Modelling Sub-processes • the task is to identify all the sub-processes that must take place to achieve the purpose of the parent process • start by identifying the normal sequence of events • list the processes • identify the error or abnormal events • add to the process list DFD - Exploding

  7. Local Data Stores • it may become apparent that a new data store is required • if only the sub-processes interface with it then add it to the exploded diagram • if other processes use it, add to the top level • if a data store on the top level DFD only interfaces with one process • remove it and place inside the exploded process DFD - Exploding

  8. Diagram Construction • the exploded process is represented by a large frame, named and numbered • on the left outside are placed the inputs • on the right outside are placed the outputs • sub-processes & local data stores are placed inside the frame DFD - Exploding

  9. Contd. • add the processes connecting them to the in/outputs • numbering the processes • n.1, n.2 etc where n is the number of the parent • numbering the data stores • continue the sequence from the top level • make sure all inputs & outputs are connected to the sub-processes DFD - Exploding

  10. Consistency Checking • check numbering correct • check no name clashes • check number of inputs and outputs are at least as many as those on the top level • if there are more check they are logically the same • flow duplication and splitting is possible DFD - Exploding

  11. Diagram Hierarchy • it is possible to explode the processes in an exploded diagram • this leads to a hierarchy of levelled DFDs DFD - Exploding

  12. Development : Low-Level DFD • Low-Level Data Flow Diagram (LL-DFD) • For each process • Low-Level DFD description • Low-Level DFD Diagram • Top-Level Data Flow Diagram (TL-DFD) • Amend your diagrams and supporting text after consistency checking with the low-level DFD’s. • Top-Level DFD description • Top-Level DFD Diagram • Context Diagram (CD-DFD) • Amend your diagrams and supporting text after consistency checking with the low-level DFD’s. • Context Diagram description • Context Diagram DFD - Exploding

  13. Document : Analysis Specification • Terms Of Reference lecture 02 • Context Diagram lecture 03 • Top-Level Data Flow Diagram lecture 04 • Top-Level DFD Support Text lecture 05 • Top-Level DFD lecture 06 • Data Flow Fragments • Low-Level Data Flow Diagrams lecture 06lecture 07 For each Top-Level process • Low-Level DFD Support Text • Low-Level DFD DFD - Exploding

  14. Summary check processes capture in/outputs check local data stores build DFD check consistent levelled hierarchy Self Study review the lecture complete 6a from the workbook can you achieve the objectives set out in slide 2? Summary & Self Study DFD - Exploding

  15. Further Reading • http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk11.doc DFD - Exploding

  16. Further Reading • Notes from Annette Marshall • http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk3.doc • http://outranet.scm.tees.ac.uk/users/u0018257/SDV/SDevWk4.doc DFD - Exploding

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