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IMS1805 Systems Analysis

Recap of the last three lectures on the importance of understanding analysis purposes, different types of models, and common issues in process, data, soft systems, and O-O modeling.

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IMS1805 Systems Analysis

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  1. IMS1805Systems Analysis Topic 3: Doing analysis (cont)

  2. Recap of last three lectures • The importance of understanding the purpose of analysis • Some important purposes: • Organisational; • Technological; • Development team • The purposes behind various types of models (FDD/DFD/ERD/O-O/Soft systems)

  3. Agenda • Aim: To develop further your skills in using analytical techniques • To identify some of the main problem areas students have in applying these techniques

  4. 1. Issues in process modelling: (a) physical vs logical models • Physical actions versus information transformations • People/places/times vs logical information events • Note: Physical models are not ‘wrong’ – unless you are asked for a logical model! • Why bother with the distinction? The importance of “seeing” pure information elements, not physical objects • Examples from tute exercise

  5. Issues in process modelling: (b) actions and data flow elements • Relating physical actions to information processes • Understanding/interpreting actions as data flow elements other than processes • Seeing the overall picture: recognising the problems arising from poor process selection and re-thinking the process • Examples from tute exercise

  6. Issues in process modelling: (c) hierarchy and abstraction in processes • The concept of hierarchy of processes • Low-level vs high-level processes • Composite (multi-process) processes vs single processes • Implications for process names • Why bother with the distinction? The importance of “seeing” both top and bottom level processes • Examples from tute exercise

  7. Issues in process modelling: (d) naming data flow elements • ‘Bad’ names vs ‘good’ names • Processes = verb + name (what transformation occurs + what data is transformed) • High-level process names vs low-level process names • Names as a clue to how clearly you are thinking • Examples from tute exercise

  8. Issues in process modelling: (e) testing your process model • Putting the pieces together for an FDD: • Every element of the diagram is a process • Every low-level (child) process is a component of its associated higher-level (parent) process • Every high-level (parent) process is fully described by its associated lower-level (child) processes • Putting the pieces together for a DFD: • Every process must have data inputs and data(/info) outputs • Every data input/output must have a process at one end and either a process, data store or external agent at the other end • All inputs must be used by a process to create all its outputs • Processes ‘fit together’ in the same levels as in the FDD • Examples from tute exercise

  9. 2. Issues in data modelling: (a) choosing your entities • ‘Things’ which are involved in or part of the system vs ‘things’ about which the system needs to store information • The first test for any entity: what are its attributes? (ie what does this system need to store as information about it (and why)?) • Seeing an entity as a table in a database • Examples from tute exercise

  10. Issues in data modelling: (b) distinguishing attributes and entities • Features which are inherently part of something (attributes) vs features which are connected/related to it.(Perhaps a different entity or an attribute of a different entity?) • The first test for any attribute: does it have attributes as well? (ie does this system need to store as information about it?) If so, should it be an entity in its own right? • Seeing an attribute as a field (column) in a database record • Examples from tute exercise

  11. Issues in data modelling: (c) identifying relationships • What connections does the system need to be able to make between entities? • Seeing a relationship as the basis for setting rules for a database to enforce about its entities • Seeing a relationship as the basis on which queries can be built between database tables • Examples from tute exercise

  12. 3. Issues in soft systems modelling: (a) identifying stakeholder positions • Do all people involved in a system have attitudes towards it OR are people neutral users who simply supply/extract information? • Do people involved in a system have ‘rights’ which should be acknowledged and taken into account? • Is it sensible to ignore people’s attitudes/rights towards a system? • Examples from tute exercise

  13. 4. Issues in O-O modelling: (a) identifying objects • How easy is it for you to identify: • Actions? • Processes? • Entities? • How easy is it for you to identify objects? • How easy is it to create objects from composites of processes and entities? • Examples from tute exercise

  14. Administration • Assignment documents • New assignment deadline • No lecture on Monday, August 29th

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