SE DFD 160412

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Data Flow Diagrams (DFD)
Software Engineering

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SE DFD 160412

  1. 1. bharat_mybooks@rediffmail.com 1 DFD: Data Flow Diagram by: Bharat V. Chawda Computer Engineering Department, BBIT, VVNagar
  2. 2. bharat_mybooks@rediffmail.com 2 Overview  A Concept  Primitive Symbols  Context Diagram  Level 1 Diagram  Decomposition  Example  Do’s and Don’ts  Shortcomings
  3. 3. bharat_mybooks@rediffmail.com 3 A Concept: Simple Example  RMS: Root Mean Square RMS Calculator 0 User I/P Data rms Validate input 1 Compute RMS 2 Valid Data Display result 3 rms rms Further Decomposition… (What is RMS?) I/P Data
  4. 4. bharat_mybooks@rediffmail.com 4 A Concept:  “A graphical representation of the flow of data through an information system, modelling its process aspects.”  Shows:  What data is Input; Who generates it: Source  What data is O/P; Who receives it: Destination/Sink  What processing is performed on data; by whom: Proc  Where data come from and go to: Data Flow  What data is stored; where: Data Store  Does not show:  Timing of processes: Executed in parallel or sequence  Different from Flowchart (Why?)
  5. 5. bharat_mybooks@rediffmail.com 5 A Concept:  Why Popular?  Easy to understand by technical and non-technical persons  Can provide high level system overview; with boundaries and connections to other systems  Can provide a detailed representation of system components  Provides hierarchy of DFDs  Top level: Most abstract: Context Diagram / Level 0 D.  Next level: Level 1 Diagram  Further levels: Level 2, 3, 4…
  6. 6. bharat_mybooks@rediffmail.com 6 Primitive Symbols for DFD  Process / Function: Circle, Rounded Rectangle  Actions performed on data: Transformed, Stored, or Distributed  Annotated with number and name of function  Name starts with verb (Except context level diagram)  Data Flow: Directed arc, Arrow  Single piece of data or logical collection of data  Annotated with name/description of data
  7. 7. bharat_mybooks@rediffmail.com 7 Primitive Symbols for DFD  External Entity: Rectangle  Source and/or Sink  Origin and/or Destination of the data  External, cos outside the system  Annotated with name (Noun)  Data Store: Open rectangle, parallel lines  Data structure, File, Table, Database  Annotated with corresponding names of data items
  8. 8. bharat_mybooks@rediffmail.com 8 Context or Level 0 Diagram  Concept:  Main steps: Identify where data is captured from: Source Identify where data is distributed to: Destination Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled
  9. 9. bharat_mybooks@rediffmail.com 9 Level 1 Diagram  Concept:  Main steps:  Identify and draw the processes that make up the Level 0 process: High level functions  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level 0 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links: Data flows [Note: It should be balanced. (What is balanced DFD?)]
  10. 10. bharat_mybooks@rediffmail.com 10 Decomposition/Level ‘n’ Diagram  Concept:  Main steps:  Identify and draw the processes that make up the Level n-1 process  Allocate descriptions to these processes  Lay out all the data flows from the Level n-1 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links: Data flows
  11. 11. bharat_mybooks@rediffmail.com 11 Ex: Food Order System  Description  Customer provides order.  System produces receipt by referring order and gives to customer.  Order is also sent to kitchen department.  Based on order, “Goods sold” and “Inventory” files are updated.  Reports for the top management regarding sales, inventory depletion (income, expenditure) are generated.
  12. 12. bharat_mybooks@rediffmail.com 12 Context or Level 0 Diagram  Main steps: Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled
  13. 13. bharat_mybooks@rediffmail.com 13 Context or Level 0 Diagram CUSTOMER
  14. 14. bharat_mybooks@rediffmail.com 14 Context or Level 0 Diagram  Main steps: Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled
  15. 15. bharat_mybooks@rediffmail.com 15 Context or Level 0 Diagram CUSTOMER KITCHEN RESTAURANT MANAGER
  16. 16. bharat_mybooks@rediffmail.com 16 Context or Level 0 Diagram  Main steps: Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled
  17. 17. bharat_mybooks@rediffmail.com 17 Context or Level 0 Diagram Food Ordering System 0 CUSTOMER KITCHEN RESTAURANT MANAGER
  18. 18. bharat_mybooks@rediffmail.com 18 Context or Level 0 Diagram  Main steps: Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled
  19. 19. bharat_mybooks@rediffmail.com 19 Context or Level 0 Diagram Food Ordering System 0 CUSTOMER KITCHEN RESTAURANT MANAGER Receipt Food Order Management Reports Customer Order
  20. 20. bharat_mybooks@rediffmail.com 20 Level 1 Diagram  Main steps:  Identify and draw the processes that make up the Level 0 process  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level 0 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links
  21. 21. bharat_mybooks@rediffmail.com 21 Level 1 Diagram 1.0 Receive and transform Customer Food Order 3.0 Update Inventory file 2.0 Update Goods Sold file 4.0 Produce Management Reports
  22. 22. bharat_mybooks@rediffmail.com 22 Level 1 Diagram  Main steps:  Identify and draw the processes that make up the Level 0 process  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level 0 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links
  23. 23. bharat_mybooks@rediffmail.com 23 Level 1 Diagram 1.0 Receive and transform Customer Food Order 3.0 Update Inventory file 2.0 Update Goods Sold file 4.0 Produce Management Reports Receipt Customer Order CUSTOMER KITCHEN Food Order RESTAURANT MANAGER Management Reports
  24. 24. bharat_mybooks@rediffmail.com 24 Level 1 Diagram  Main steps:  Identify and draw the processes that make up the Level 0 process  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level 0 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links
  25. 25. bharat_mybooks@rediffmail.com 25 Level 1 Diagram 1.0 Receive and transform Customer Food Order 3.0 Update Inventory file 2.0 Update Goods Sold file 4.0 Produce Management Reports Receipt Customer Order CUSTOMER KITCHEN Food Order RESTAURANT MANAGER Management Reports D1 Goods Sold File D2 Inventory File
  26. 26. bharat_mybooks@rediffmail.com 26 Level 1 Diagram  Main steps:  Identify and draw the processes that make up the Level 0 process  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level 0 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links
  27. 27. bharat_mybooks@rediffmail.com 27 Level 1 Diagram 1.0 Receive and transform Customer Food Order 3.0 Update Inventory file 2.0 Update Goods Sold file 4.0 Produce Management Reports Receipt Customer Order CUSTOMER KITCHEN Food Order RESTAURANT MANAGER Management Reports Goods Sold Inventory Data Goods Sold Data Inventory Data Daily Goods Sold Amount Daily Inventory Depletion Amount D1 Goods Sold File D2 Inventory File
  28. 28. bharat_mybooks@rediffmail.com 28 Level ‘n’ Diagram  Main steps:  Identify and draw the processes that make up the Level n-1 process  Allocate descriptions to these processes  Lay out the sources/sinks and data flows from the Level n-1 diagram  Draw in any data stores used in the process  Link the new processes and data stores with named data links
  29. 29. bharat_mybooks@rediffmail.com 29 Level 2 Diagram 4.0 Produce Management Reports Management Reports Daily Goods Sold Amount Daily Inventory Depletion Amount 4.1 Access Goods Sold and Inventory Data 4.2 Aggregate Goods Sold and Inventory Data 4.3 Prepare Management Reports Daily Goods Sold Amount Daily Inventory Depletion Amount Goods Sold data Inventory Data Aggregated Data Management Reports
  30. 30. bharat_mybooks@rediffmail.com 30 Level 3 Diagram 4.3 Prepare Management Reports Aggregated Data Management Reports 4.3.1 Format Management Reports Aggregated Data 4.3.2 Print Management Reports Formatted Data Management Reports
  31. 31.   Do’s and Don’ts Processes must have both Inputs and Outputs No process can have only Inputs or only Outputs bharat_mybooks@rediffmail.com 31
  32. 32.   Do’s and Don’ts  All flows to Data store must move through a Process bharat_mybooks@rediffmail.com 32
  33. 33.   Do’s and Don’ts  All flows to External Entity must move through a Process bharat_mybooks@rediffmail.com 33
  34. 34. bharat_mybooks@rediffmail.com 34 Shortcomings of DFD  Can be Imprecise  May not capture the entire functionality  What happens if inputs are wrong; if book not found  Control aspects not defined  Order: inputs are consumed, output r produced: X  Order: different processes are executed: X  Decomposition: Subjective  How to arrive at successive level; Up to how much level: subjective; depends upon analyst  Same problem  Multiple DFDs possible  Decomposition: No specific guidance
  35. 35. 35 To be continued… bharat_mybooks@rediffmail.com

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