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System Development Tools, Techniques and Methods

System Development Tools, Techniques and Methods . Structured Process Modelling. 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 .

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System Development Tools, Techniques and Methods

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

  2. 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. 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. 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. Current physical process model • two volunteers please • one student • one bar steward

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

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

  8. 1 Barsteward Serve bottle of Bud 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

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

  10. Servebottleof Bud 1 Barsteward Bottle of Bud Student Material Flow • A newish, non-purist representation of the movement of material

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

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

  14. 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. Levelling - Graphically Context Level 1 Level 2 L e v e l 3

  16. 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. Example of levelling • Level 0 • Video Hire System • Level 1 • Process 1 Administer Membership • Level 2 • Process 1.1 Receive membership application

  18. 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. 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. 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. Health warning • Process modelling only makes sense when you do it (it seems trivial otherwise)

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