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CSE1204 - Information Systems 1

CSE1204 - Information Systems 1. Process Modelling Using Data Flow Diagrams – Building and Levelling Them; Process Modelling Using Function Decomposition. Example system:. a generic warehouse-inventory information system. Levelling Data Flow Diagrams.

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CSE1204 - Information Systems 1

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  1. CSE1204 - Information Systems 1 Process Modelling Using Data Flow Diagrams – Building and Levelling Them; Process Modelling Using Function Decomposition

  2. Example system: • a generic warehouse-inventory information system Monash University, SIMS, Semester One, 2005

  3. Levelling Data Flow Diagrams • any "real" system is too large to represent as a single data flow diagram • the solution is to decompose the system into a hierarchy of levels of processing • the process model of the system then consists of a set of levelled data flow diagrams • levelling of DFDs improves their readability and usefulness as a communication tool Monash University, SIMS, Semester One, 2005

  4. Levelling of DFDs Levelling creates a hierarchical decomposition of the processing within the system • Context diagram • Level 0 diagram • Level 1 diagrams • Level 2 diagrams . . . • Level n diagrams Monash University, SIMS, Semester One, 2005

  5. Context Diagram • the highest level data flow diagram is the context diagram • the context diagram shows the interaction of the system with its environment in terms of data flows • the context diagram defines the boundary of the system (the scope of the system) • only the data flows which leave the system and the data flows which come from outside the system are shown Monash University, SIMS, Semester One, 2005

  6. Context Diagram • the entire system is represented as a single process • all external agents (sources and sinks) are shown • no data stores are shown: they are inside the boundary of the system EASY GO HOTEL Monash University, SIMS, Semester One, 2005

  7. Example Context Diagram Sales Order System sales order Suppliers purchase order goods returned supplier delivery Inventory System goods unavailable notice shipping slip checked supplier invoice Accounts Department Warehouse Monash University, SIMS, Semester One, 2005

  8. Level Zero Diagram • the level zero data flow diagram is the diagram at the level immediately below the context diagram • it "expands" the single process on the context diagram to show the major, high-level processes (or functions) within the system 1.0 4.0 2.0 3.0 Monash University, SIMS, Semester One, 2005

  9. Level Zero Diagram • all external agents (sources and sinks) are included because the level zero diagram, like the context diagram, represents the entire system • the number of each process ends in .0 which corresponds to the level of the diagram: e.g. 1.0, 2.0, 3.0 etc. often just 1, 2, 3 etc. are used Monash University, SIMS, Semester One, 2005

  10. Example Level Zero Diagram Order Entry System Suppliers purchase order sales order 2.0 Monitor Stock levels 3.0 1.0 supplier delivery Fill Sales Orders Accept Deliveries out of stock notice Stock file shipping slip Accounts Department checked supplier invoice Warehouse Monash University, SIMS, Semester One, 2005

  11. Levelling DFDs Context diagram 1 2 3 1.1 Level zero diagram 1.2 Monash University, SIMS, Semester One, 2005 Diagram 1 (at Level 1)

  12. Level 1 diagrams • a set of data flow diagrams is created at Level 1 • there is one Level 1 diagram for each of the processes at Level zero • each diagram decomposes a Level zero process into several processes 2.4 2.3 2.1 2.5 2.2 Monash University, SIMS, Semester One, 2005

  13. Level 1 and lower level diagrams • each Level 1 diagram and diagrams at lower levels (e.g. Level 2, Level 3) show only a part of the processing • Level 1 processes are numbered 1.1, 1.2, 1.3, and 2.1, 2.2, 2.3 etc • that part is shown in more detail than on the Level zero diagram • no external agents are shown on a Level 1 or lower diagrams, as the entire system is not being represented Monash University, SIMS, Semester One, 2005

  14. CUSTOMERS SUPPLIERS Example Level zero diagram p.o. number Customer details Product details p.o. invoice product product delivered qty product qty product holding INVENTORY order qty 1 product holding Record and Invoice Sales product order qty 2 delivery qty Maintain Product Inventory SALES ORDERS customer invoice product order qty Monash University, SIMS, Semester One, 2005

  15. Example Level 1 diagram 1.2 INVENTORY Customer details Check Stock Available 1.1 product holding Check Customer Credit product qty INVOICES product customer credit status available qty SALES ORDERS Product details 1.4 1.3 Create Sales Invoice customer invoice product qty Record Sales Demand Monash University, SIMS, Semester One, 2005

  16. Levelling of DFDs Context Level 0 1 2 3 4 1.3 4.2 Level 1 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.3 Level 2 1.1.1 1.1.2 3.2.1 3.2.2 Monash University, SIMS, Semester One, 2005

  17. References • WHITTEN, J.L., BENTLEY, L.D. and DITTMAN, K.C. (2001) 5th ed., Systems Analysis and Design Methods, Irwin/McGraw-HilI, New York, NY. Chapters 8 • HOFFER, J.A., GEORGE, J.F. and VALACICH (2005) 4th ed., Modern Systems Analysis and Design, Benjamin/Cummings, Massachusetts. Chapter 7 Monash University, SIMS, Semester One, 2005

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