Software Engineering Data flow diagrams

1. Software Engineering Data flow diagrams

2. Using Data Flow Diagrams

3. Theory Data is your main player Data will start at a source Data will end at a sink Data will change at a process Data will be stored or retrieved at a data store Your must have the right tool box GRAMMER is your camera Balance is the rule of thump Abstract diagram Rules and restrictions

5. Advantages of DFD • Freedom from involving with technical implementation too early • Provide information inter-relatedness of systems and sub-systems • Can be used as a tool for communicating with users (but, users must have some knowledge about the DFD) • Analysis of a proposed system to determine all important data and process have been defined

6. Four Basic Symbols Used in DFD • Entity • is considered as EXTERNAL to the system • e.g., a department, a person, or a business • should be named with a “noun” • can be used more than once in order to avoid crossing • Data Flow • shows movement of data • should be named with a “noun” • each arrow represents only one data flow

7. Four Basic Symbols Used in DFD • Process • represents a process • should use verb-adjective-noun format for naming all processes • e.g., “Add Inventory Record” must record also have unique number which represent each process and indicate its level • Data • may represent database or filing cabinet • should be named with a “noun” • Note: temporary data stores, scratch paper, or temporary computer files are not included

8. Process for Developing DFD • Make a list of business activities and use it to determine: • External entities • Data Flows • Processes • Data Stores • Draw a Context diagram which shows only a single process (represent the entire system), and external entities • Draw a Diagram-0 (Level-0 diagram) • shows general processes • shows data stores • Draw child diagrams (Level-1 diagram) for each of the process in Diagram-0

9. Process for Developing DFD • Check for errors and all labels to ensure that they are meaningful (ref. Fig 9.4, 9.5, and 9.6) • Develop physical data flow diagram from the logical data flow • Distinguish between manual & automated processes • Describe actual files & reports by name • Add controls to indicate when error occur • Partition the physical data flow diagram by grouping parts of the diagram from implementation purpose

10. Logical vs Physical DFD • Logical diagrams: • show how the business operates, not how the system will be implemented • describe each event and data required • Physical diagrams: • show how the system will be implemented • e.g., details about hardware, software, files and people involved (Figure 9.10)

11. Characteristics of Physical DFD • Determine manual or automated processes • Provide more details than logical DFD • Sequence processes that have to be done in a particular order • Identify temporary file(s) required • Use actual names of files and printouts

12. Partitioning DFD • Analyzing each process to determine whether it should be a manual or automated process • Reasons for partitioning • Different user groups: Different group of users may work on different set of data which require different interface • Efficiency: Several batch processes may be combined into one program to save time required • Security: Some process (program) is only for a certain group

29. System contexts • The boundaries of the system must be established to determine what must be implemented • These are documented using a description of the system context. This should include a description of the other systems which are in the environment • Social and organizational factors may influence the positioning of the system boundary

30. Auto-teller system context

35. Online Order processing problem statement Each on-line order is processed for release to the manufacturing floor. Release is generally dependent upon approval of the designated form of payment. Credit card orders move faster while orders paid by other methods generally take longer. Once payment is confirmed, the order will be released for production. The order is then sent to the company distributor of UIGC corporation, items . Once received by the distribution facility, the order will be prepared and released for shipping. Delivery prep is normally completed within one day of the date production is complete. However, larger orders and orders requiring special handling and refrigerating may take longer. Each order is shipped and will be in route to its ship-to destination as of the "Ship Date" that is indicated. Delivery time varies based on the shipping option chosen at the time of order entry. Each order will generally reach its intended destination within 15-30 business days of the "Ship Date" noted

36. 1-Smartly Identify different grammatical types in sentences Each on-line order is processed for release to the manufacturing floor. Release is generally dependent upon approval of the designated form of payment. Credit card orders move faster while orders paid by other methods generally take longer. Once payment is confirmed, the order will be released for production. The order is then sent to thecompany distributor of UIGC corporation items . Once received by the distribution facility, the order will be prepared and released for shipping. Delivery prep is normally completed within one day of the date production is complete. However, larger orders and orders requiring special handling and refrigerating may take longer. Each order is shipped and will be in route to its ship-to destination as of the "Ship Date" that is indicated. Delivery time varies based on the shipping option chosen at the time of order entry. Each order will generally reach its intended destination within 15-30 business days of the "Shipping”.

37. Build the analytical table: Sentence # Nouns Analysis Verbs Analysis 1 Online order Sub-class Sub –system Data flow Process Release Manufacture Process,Ass. Process Process,Ass 2 Payment Data flow Super-Class ERM Entity Approve Designate Process Process 3 Credit card Order Data flow Sub-class Confirm Release Produce Process Process Process 4 Company distributor UIGC External entity External entity Send Process 5 Distribution facility External entity Receive Prepare Release Ship Process,Ass. Process,Ass. Process,Ass. Process,Ass. 6 Deliver complete Process,Ass. Process,Ass. 7 Large order Sub-class Data flow Require Refrigerate Handle Pro, Ass. Process,Ass. 8 Ship-date Destination Attribute Class Ship Route Indicate Process,Ass Process,Ass. Process,Ass. 9 Choose Enter data Process,Ass. Process,Ass. 10 Intended destination Attribute Reach Process,Ass.

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41. More Examples on Data Flow Diagrams

42. Data Flow Diagram (DFD) • It is designed to show how a system is divided into smaller portions, and • to highlight the flow of data between those parts.

43. Context-Level Data Flow Diagram Showing Project Scope for Purchasing Fulfillment System

44. Comparison of DeMarco & Yourdan and Gane & Sarson DFD Symbol Sets

45. Differences between Sources/Sinks and Processes (a) Improperly Drawn DFD

46. Differences between Sources/Sinks and Processes (b) Proper Use of a Process

47. Context Diagram of Hoosier Burger’s Food Ordering System

48. Level-0 DFD of Hoosier Burger’s Food Ordering System

49. Level-1 Diagram Showing Decomposition of Process 1.0 from the Level-0 Diagram

50. Level-1 Diagram Showing the Decomposition of Process 4.0 from the Level-0 Diagram