SDLC – Models

Software Development Life Cycle Model

• A framework containing the processes, activities and the tasks involved in the development, operation and maintenance of a software product spanning the life of the system from the definition of it’s requirements to the termination of it’s use (ISO/IEC 12207)

SDLC Models

• Waterfall model

• Spiral model

• Prototype model

• Rapid application development model

Waterfall Model

• Also known as ‘classic life cycle model’, ‘linear sequential model’

• This model suggests a systematic and sequential approach to software development that begins at requirements analysis and progresses through all life cycle phases sequentially

Waterfall Model (Cont’d)

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Waterfall Model (Cont’d)

• Development activities carried out sequentially

• Review and approval of each phase outputs

• Model does not permit going back and forth

• If any defect found, go back to the originating phase and start traversing sequentially all over again

Waterfall Model (Cont’d)

Suitable for projects where –

• Requirements are clearly defined

• Small and medium term duration

• Stable technology

• Familiarity with the domain and development environments

Waterfall Model (Cont’d)

Advantages:

• Projects under control

• Pre-defined outputs at every phase

• Tracking changes is easy

• Early identification of slippages, if any

Waterfall Model (Cont’d)

Disadvantages:

• In real life, customer requirements do change

• Customer appraisal of completed work - not feasible always

• Phases can not run concurrently

Spiral Model

In a spiral model, software is developed in a series of ‘incremental’ releases

The spiral model is divided in to a number of framework activities or task regions

Spiral Model (Cont’d)

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Spiral Model (Cont’d)

• Suitable for large projects with multi-location implementation

• Each Spiral consists of a deliverable product

• Feedback of each spiral is incorporated in the next spiral

• Customer can start using the system after every spiral

• Each Spiral consists of a waterfall model

Spiral Model (Cont’d)

Advantages:• Useful for large projects• Customer requirements evolve over a period• Early availability of usable systemDisadvantages:• Total blue print should be available in the

beginning• Basic concepts in the underlying layer can NOT

be changed

Prototype Model

A prototype model is a representation of a real life situation, which can be evaluated by the user

A prototype is developed based on the initial understanding of the customer requirements

A visible working prototype helps customer to define the requirements

Prototype Model (Cont’d)

Prototype model is used for eliciting customer requirements as well as identifying user – machine interaction

Prototype model is used in product development or for developing a new application for a customer

Prototype Model (Cont’d)

Advantages :• Can be used when customer is not sure about what

he wants• Faster way of finalising the requirements• Useful for new technologies and domains

Disadvantage :• A prototype if used in a production environment,

may lack quality or maintainability

Rapid Application Development Model

RAD is a high speed adaptation of linear sequential model by using component based construction

RAD enables creation of fully functional software within a very short time

RAD Model (Cont’d)

Advantages :• Very short cycle time• Use of working components lead to minimum

defects

Disadvantages :• Not useful for systems that can NOT be properly

modularised• Fine-tuning the existing components is NOT

possible