Mis 5i565y

SYSTEM DEVELOPMENT MODELS: Specify how the activities of development process are organized in the total system development effort.”

WATERFALL MODEL:  Requirements phase - in which the requirements for the software are gathered and analyzed, to produce a complete and unambiguous specification of what the software is required to do  Detailed Design phase - where the detailed implementation of each component is specified.  Code and Unit Test phase - in which each component of the software is coded and tested to that it faithfully implements the detailed design.  Software Integration phase - in which progressively larger groups of tested software components are integrated and tested until the software works as a whole.  System Integration phase - in which the software is integrated to the overall product and tested.  Acceptance Testing phase, where tests are applied and witnessed to validate that the software faithfully implements the specified requirements. Software specifications will be products of the first three phases of this lifecycle model. The remaining four phases all involve testing the software at various levels, requiring test specifications against which the testing will be conducted as an input to each of these phases Advantages:  Enforced discipline through documents  no phase is complete until the docs are done & checked by SQA group  concrete evidence of progress  Testing is inherent in every phase  continuously as well as at end of phases  Verification of the Software is easy.  Easy to understand, easy to use  Provides structure to inexperienced staff  Sets requirements stability  Good for management control (plan, staff, track) Disadvantages:  Document-driven model  customers cannot understand these – imagine an architect just showing you a textual spec!  first time client sees a working product is after it has been coded. Problem here? – leads to products that don’t meet customers needs

 Assumes feasibility before implementation  re-design is problematic  works best when you know what you’re doing – when requirements are stable & problem is well-known  All requirements must be known upfront  System can be frozen before the design begins  Little opportunity for customer to preview the system (until itmay be too late) PROTOTYPING

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Starts with only a general idea of requirements, and develops models of the system ‘until it’s right’ Preliminary model built rapidly and inexpensively Four-step process Identify the ’s basic requirements Develop an initial prototype Use the prototype Revise and enhance the prototype Especially useful in deg a interface Advantages:  Speeds up the development approach  Gives the s the opportunity to clarify their information requirements  Useful in the development of decision systems and executive information systems Disadvantages:  Replaces the systematic analysis and design stages of the SDLC - quality may be sacrificed

 Can result in an excess of iterations

Advantages Customers can “see” the system requirements as they are being gathered A more accurate end product Unexpected requirements accommodated Allows for flexible design and development Lower overall development costs when requirements change frequently Limitations Prototyping can lead to false expectations. Prototyping can lead to poorly designed systems

END DEVELOPMENT – –

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s perform ad hoc programming to solve business problems Factors that drive the trends toward increased end- computing and end- development  More powerful, inexpensive desktop hardware  Increasingly diverse software capabilities  Increasingly computer literate population  Backlog of IS projects  Apparent cost savings End-s (usually) don’t produce adequate documentation or perform adequate testing Security may be breached

SPIRAL MODEL

STEPS:  Define the problem with as much detail as possible by interviewing the client and potential s of the system, as well as, studying any existing system.  A preliminary design is created for the new system.  A first prototype of the new system is constructed from the preliminary design and is a scaled down version of the final product  A second prototype is derived by the following procedure o Evaluate the first prototype for strengths, weaknesses and risks nd

o Define the requirements of the 2 prototype nd

o Plan and design the 2 prototype nd

o Construct and test the 2 prototype  At this point the customer may decide to scrap the whole project if the risk is too high. o Development cost overruns o Operating-cost miscalculation o Other factors that might result in a substandard product  Evaluate the current prototype in the same way as the previous prototype and create another one if needed.

 Iterate the proceeding steps until the customer is satisfied that the current prototype represents the final product.  Construct the final system.  The final system is thoroughly evaluated and tested and routine maintenance is carried out for the life of the product.

Advantages Risk assessment s see the system early because of rapid prototyping tools Limitations Time spent for evaluating risks too large for small or low-risk projects The model is complex Risk assessment expertise is required

Sdlc strengths & weakness Strengths

Weaknesses

Control.

Increased development time.

Monitor large projects.

Increased development cost.

Detailed steps.

Systems must be defined up front.

Evaluate costs and completion targets. Rigidity. Documentation.

Hard to estimate costs, project overruns.

Well defined input.

input is sometimes limited.

Ease of maintenance. Development and design standards. Tolerates changes in MIS staffing.