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

2. Monash University, SIMS, Semester One, 20052 Example system: a generic warehouse-inventory information system a generic warehouse-inventory information system

3. Monash University, SIMS, Semester One, 20053 Levelling Data Flow Diagrams any "real" system is too large to represent as a single data flow diagram 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 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 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 levelling of DFDs improves their readability and usefulness as a communication tool

4. Monash University, SIMS, Semester One, 20054 Levelling of DFDs Context diagram Context diagram Level 0 diagram Level 0 diagram y Level 1 diagrams y Level 2 diagrams... y Level n diagrams Levelling creates a hierarchical decomposition of the processing within the system

5. Monash University, SIMS, Semester One, 20055 Context Diagram the highest level data flow diagram is the 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 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) 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 only the data flows which leave the system and the data flows which come from outside the system are shown

6. Monash University, SIMS, Semester One, 20056 Context Diagram the entire system is represented as a single process the entire system is represented as a single process all external agents (sources and sinks) are shown all external agents (sources and sinks) are shown no data stores are shown: they are inside the boundary of the system no data stores are shown: they are inside the boundary of the system EASY GO HOTEL

7. Monash University, SIMS, Semester One, 20057 Example Context Diagram Inventory System Suppliers Sales Order System Warehouse sales order goods unavailable notice purchase order supplier delivery shipping slip checked supplier invoice Accounts Department goods returned

8. Monash University, SIMS, Semester One, 20058 Level Zero Diagram the level zero data flow diagram is the diagram at the level immediately below the context 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 it "expands" the single process on the context diagram to show the major, high-level processes (or functions) within the system 1.0 2.0 3.0 4.0

9. Monash University, SIMS, Semester One, 20059 Level Zero Diagram all external agents (sources and sinks) are included because the level zero diagram, like the context diagram, represents the entire system 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: 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

10. Monash University, SIMS, Semester One, 200510 Example Level Zero Diagram Monitor Stock levels Suppliers Order Entry System Warehouse sales order out of stock notice purchase order supplier delivery shipping slip checked supplier invoice Accounts Department Fill Sales Orders Accept Deliveries 1.0 2.0 3.0 Stock file

11. Monash University, SIMS, Semester One, 200511 Levelling DFDs 1 2 3 1.1 1.2 Context diagram Level zero diagram Diagram 1 (at Level 1)

12. Monash University, SIMS, Semester One, 200512 Level 1 diagrams a set of data flow diagrams is created at Level 1 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 there is one Level 1 diagram for each of the processes at Level zero each diagram decomposes a Level zero process into several processes each diagram decomposes a Level zero process into several processes 2.1 2.2 2.3 2.4 2.5

13. Monash University, SIMS, Semester One, 200513 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 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 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 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 no external agents are shown on a Level 1 or lower diagrams, as the entire system is not being represented

14. Monash University, SIMS, Semester One, 200514 Example Level zero diagram CUSTOMERS SALES ORDERS INVENTORY p.o. number product order qty p.o. invoice delivery qty customer invoice Product details product qty Customer details product holding product order qty product holding product delivered qty product order qty Record and Invoice Sales 1 Maintain Product Inventory 2 SUPPLIERS

15. Monash University, SIMS, Semester One, 200515 Example Level 1 diagram Customer details Product details product qty SALES ORDERS customer credit status product qty product INVENTORY product holding available qty INVOICES customer invoice Check Customer Credit 1.1 Record Sales Demand 1.3 Check Stock Available 1.2 Create Sales Invoice 1.4

16. Monash University, SIMS, Semester One, 200516 1.34.2 1.1.11.1.23.2.13.2.2 Context Level 0 Level 1 Level 2 1234 1.11.22.12.23.13.24.14.3 Levelling of DFDs

17. Monash University, SIMS, Semester One, 200517 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 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. HOFFER, J.A., GEORGE, J.F. and VALACICH (2005) 4th ed., Modern Systems Analysis and Design, Benjamin/Cummings, Massachusetts. Chapter 7 Chapter 7