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Systems Development Methodologies. Content. What are methodologies for systems development? Advantages and disadvantages of methodologies Physical and logical approaches Comparison of types of methodologies (separate lecture slides). 1. Systems development methodologies.
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Content • What are methodologies for systems development? • Advantages and disadvantages of methodologies • Physical and logical approaches • Comparison of types of methodologies (separate lecture slides)
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
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
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
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
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
4.1 Types of methodology • Process driven methodologies • Data driven methodologies • User driven methodologies • Hybrid methodologies - SSADM
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
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
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 - Checkland’s SSM
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?
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.
