Systems Development Methodologies

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Systems Development Methodologies
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Content

1. What are methodologies for systems development?
2. Advantages and disadvantages of methodologies
3. Physical and logical approaches
4. Comparison of types of methodologies (separate
   lecture slides)

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1. Systems development methodologies

• a collection of procedures, techniques, tools and
  documentation aids which will help systems
  developers in their efforts to implement a new IS
• consist of phases and sub-phases to assist
  planning, management and control of projects
• techniques are ways of refining a given activity
  in a system development process, each technique
  may involve using one or more tools

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2.1 Advantages of methodologies

• they produce better ISs
• they provide a better development process
• they use standard methods to produce systems that
  are easier to maintain and improve

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2.2 Disadvantages of methodologies

• some have too little scope
• some are not properly thought out
• some do not consider the work or social context
  of the system
• methodologies do not guarantee success
• some are only tailored to large, complex
  organisations
• better at designing transaction processing
  systems than MIS?
• prototyping and 4GLs do not always fit neatly
  with formal methodologies

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3.1 The logical approach

• the logical design is carried out first
• it is the paper based system
• it defines what the system is supposed to do and
  the data items it deals with
• concerned with the what, rather than the how

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3.2 The physical approach

• the physical design is carried out last
• it is the actual computer system which will
  support the logical design
• concerned with the how, rather than the what

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4.1 Types of methodology

• Process driven methodologies
• Data driven methodologies
• User driven methodologies
• Hybrid methodologies - SSADM

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4.1.1 Process driven

• The systems development lifecycle (SDL) can be
  viewed as process driven
• concentrates on how data is processed
• structured analysis breaks the process down into
  phases and stages
• most structured analysis and design methodologies
  are process driven
• aids analysis of manual processes
• appropriate where small databases are required
• examples - Yourdon, STRADIS

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4.1.2 Data driven

• concentrates on the data processed
• data analysis is more suitable for database
  design
• these techniques are more appropriate for large
  projects
• example - Information Engineering
• data needs are identified before processing
  options

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4.1.3 User driven

• Soft Systems Methodology - people oriented
  approach
• SSM is a way of analysing the problem situation
  in open systems (organisations)
• a way of tackling unstructured and poorly defined
  problems in the real world
• may produce more effective system but less
  efficient in terms of data handling
• example - Checklands SSM

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4.1.4 Process versus data driven

• a company manually analyses overdue payments
  according to the number of days the debt is
  outstanding (0-30, 31-60, 61-90, 91)
• process driven analysis would automate the
  classification process with no information being
  left on file
• data driven analysis would store the input data
  so it could be used for a number of potential
  uses
• which of the above approaches would be most
  suitable and why?

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• Data or the type of data used is unlikely to
  change BUT the uses to which it will be put, on
  the other hand, are likely to alter.