1. Slide 1 of 24 System Development Tools, Techniques and Methods Structured Process Modelling

2. Slide 2 of 24 What we will cover Process Modelling in principle Data Flow Diagrams in principle Symbols and Semantics Process Modelling in action Data Flow diagrams in practice Other process modelling techniques

3. Slide 3 of 24 Context Diagrams and DFDs Symbols System (for context only) External entity Data Flow Process Data Store System boundary (Material Flow) Definitions in a moment

4. Slide 4 of 24 When process models are used Current physical the how of now Current logical the what of now Proposed logical the what of the new Proposed physical the how of the new

5. Slide 5 of 24 Current physical process model two volunteers please one student one bar steward

6. Slide 6 of 24 External Entity Person, organisation or system outside the system being considered Communicates only with system process via data flows Student Serve bottle of Bud 1Bar steward Request for bottle of Bud Student

7. Slide 7 of 24 Data Flow The direction of flow of data from source to recipient Always has a description Serve bottle of Bud 1Bar steward Request for bottle of Bud Student Request for bottle of Bud Key element in determining data needed by and in system

8. Slide 8 of 24 Process where something happens to data (transformed, validated, stored …) always has a number always has a description (strong verb, strong noun, maybe qualifier) always has a location/executor 1Bar steward Serve bottle of Bud

9. Slide 9 of 24 Data Store a location where data is stored may be manual or computer (M or D) always has a number and descriptor Till M1 Serve bottle of Bud 1Bar Steward Till M1 Money offered Change notification

10. Slide 10 of 24 Material Flow A newish, non-purist representation of the movement of material Student Serve bottle of Bud 1Bar steward Bottle of Bud

11. Slide 11 of 24 System (context only) Represents the system as a whole may include non-computer functions shows no detail of internal processes or data stores used only for context diagrams UCAS Admissions System

12. Slide 12 of 24 Oversimple context diagram BACS Money and account details Employee Timesheet Personal and account details Money Tax rules NI rules Other legal stuff Statutory bodies Payroll System Payslip Statutory payments and account details

13. Slide 13 of 24 Another Context Diagram Customer Video Hire System Membership Application Request Membership Details Returned Video Fee Hire Video Membership Application Response Membership card

14. Slide 14 of 24 Levelling Top Level - Context diagram (also known as Level 0 DFD) Next level - Level 1 DFD Next level - Level 2 DFD and so on you are unlikely to need more than 3! Numbering of lower level processes links processes between levels

15. Slide 15 of 24 Levelling - Graphically Context Level 1 Level 2 (L1 Process 1) Level 3 L2 Process 1.1 Level 3 L2 Process 1.2 Level 3 L2 Process 1.3 Level 3 L2 Process 1.4 Level 3 L2 Process 1.5 Level 3 L2 Process 1.6 Level 2 L1 Process 2 Level 3 L2 Process 2.1 Level 3 L2 Process 2.2 Level 3 L2 Process 2.3 Level 3 L2 Process 2.4 Level 3 L2 Process 2.5 Level 3 L2 Process 2.6 Level 2 L1 Process 3 Level 3 L2 Process 3.1 Level 3 L2 Process 3.2 Level 3 L2 Process 3.3 Level 3 L2 Process 3.4 Level 3 L2 Process 3.5 Level 3 L2 Process 3.6 Level 2 L1 Process 4 Level 3 L2 Process 4.1 Level 3 L2 Process 4.2 Level 3 L2 Process 4.3 Level 3 L2 Process 4.4 Level 3 L2 Process 4.5 Level 3 L2 Process 4.6 Level 2 L1 Process 5 Level 3 L2 Process 5.1 Level 3 L2 Process 5.2 Level 3 L2 Process 5.3 Level 3 L2 Process 5.4 Level 3 L2 Process 5.5 Level 3 L2 Process 5.6 Level 2 L1 Process 6 Level 3 L2 Process 6.1 Level 3 L2 Process 6.2 Level 3 L2 Process 6.3 Level 3 L2 Process 6.4 Level 3 L2 Process 6.5 Level 3 L2 Process 6.6 Context Level 1 Level 2 Level 3Level 3

16. Slide 16 of 24 Textual descriptions Every symbol represented on a process model should have a more detailed textual description linked to it Can be achieved in CASE tool Can be achieved with other, linked text (which is what you will do for your assignment) Provides explanatory detail

17. Slide 17 of 24 Example of levelling Level 0 Video Hire System Level 1 Process 1Administer Membership Level 2 Process 1.1Receive membership application

18. Slide 18 of 24 Data dictionary A precise and unambiguous way of storing data about the data identified in data flows and data stores on DFDs Links DFDs and ERMs (you will understand more about this before Christmas) Provides the basis for ER Modelling Needed for SAD assignment 2 – see Britton and Doake’s Structure Analysis book, Chapter 4

19. Slide 19 of 24 Problem/Requirements list A numbered list of all the problems with the current system and (usually hence) requirements of a new system Does not differentiate between whether issue is a problem or a requirement Serves as a check-list when conceiving and designing new system Helps to prevent problems and requirements becoming lost in the depths of analysis and design methods

20. Slide 20 of 24 Things we haven’t covered rules for building models “sensibleness” checks for DFDs Britton and Doake Chapter 4 detail of textual descriptions Tutorials, self guided study, Valachi, George and Hoffer and assignment

21. Slide 21 of 24 Health warning Process modelling only makes sense when you do it (it seems trivial otherwise)