Tietojärjestelmien peruskurssi Tietojärjestelmien suunnittelun elinkaarimalli

Systems development life cycle (SDLC) F Historical perspective of information systems development (ISD): u prevalent up to the 1980s u basis for many of today’s methodologies u in the 1950s and 1960s no well-accepted formalised methodology to develop data processing systems u computing was associated with scientific applications

SDLC u Few practical guidelines for develop systems for commercial application u oriented towards operational activities u keeping files u producing reports and documents (EDP) u company payroll; copying, retrieving, filing, sorting, checking, analysing, calculating and communicating

Historical background Comp. C C user u P u P O programmer System.anal Operator Technical analyst Business analyst

Cont. F Mismatch between users and programmers F hard to express and identify needs F inflexible F difficult to use F lack of documentation F Out of this terror the SDLC evolved

SDLC F Background in Simon’s IDC-model F Seven steps u feasibility study u systems investigation u systems analysis u systems design u implementation u review and maintenance

SDLC F Often referred to as u conventional systems analysis u traditional systems analysis u the systems development life-cycle (SDLC) u the waterfall modfel F The term life-cycle indicates an iterative approach

Feasibility study F Looks at the present systems F the requirements it was intended to meet F problems in requirement meeting F new requirements F For each of these a description is given in terms of technical, human, organisational and economic costs and benefits of developing and running the system F a proposed system must be feasible

A proposed system must be feasible F Legally (national/international and company law) F organisationally and socially F technically F economically F  recommended solution

After decision to proceed - Systems investigation F Fact finding phase u functional requirements of the system of existing S u requirements of new system/altered solutions u any constraints u range of data and type and volume u exception conditions u problems of present working methods

Systems investigation F Documentation aids u flow charts u organisation chart u manual documentation specifications u grid chart (people vs. machine)

System analysis F Analysis of present system u why is there a problem? u Why were certain work methods adopted u are there alternative methods u what are the likely growth rates of data

Systems design F Design of both computer and manual parts u input data u output of the system u processes u structure of the computer and manual files u security and back-ups u systems testing and implementation

Implementation F New programs? Written and tested F new hardware? Purchased and installed F quality controls F operations and user manuals

Review and maintenance F Reason for deciding to abandon

Strengths of SDLC F A series of sequenced phases F a series of techniques including ways of evaluating costs and benefits F a series of tools, e.g. project management tools F training scheme F philosophy

Weaknesses of SDLC F Failure to meet the needs of management F unambitious systems design F instability and inflexibility F user dissatisfaction F problems with documentation F lack of control F incomplete system F application backlog F maintenance workload F problems with the ideal approach