Spiral Model Iterative enhancement Model

1. Spiral ModelIterative enhancement Model

2. Topics • Spiral model • Iterative enhancement model

3. Spiral Model: • It is an iterative model. • The activities in this model are organized like a spiral. The spiral has many cycles. • The radial dimension in spiral model represents the cumulative cost incurred in accomplishing the steps to date. • The angular dimension represents the progress made in completing each cycle of the spiral.

4. Each cycle of the spiral begins with the identification of the objectives for that cycle, the different alternatives that are possible for achieving the objectives and constraints that exist. • The next step is to evaluate the alternatives for achieving the objectives and constraints that exist. The focus of evaluation in this step is based on the areas of uncertainty that are significant sources of project risk. • The next step is to develop strategy for resolving the risk. This may involve prototyping, simulation and benchmarking.

5. Once the risks are evaluated, the next step is developing the software keeping in mind the risks. • Finally the next stage is planned.

7. Advantages: • It focuses early attention on options involving the reuse of existing software. • It provides a mechanism for incorporating software quality objectives into software product development. This mechanism derives from the emphasis on identifying all types of objectives and constraints during each round of the spiral.

8. It focuses on eliminating errors and unattractive alternatives early. The risk analysis, validation, and commitment steps cover these considerations. • It provides a framework for integrated hardware-software system development. The focus on risk management and on eliminating unattractive alternatives early and inexpensively is equally applicable to hardware and software.

9. Dis-advantages: • Applied differently for each application. • Risk of not meeting budget or schedule. • No particular beginning or ending of a phase.

10. Iterative enhancement Model: • The iterative enhancement life cycle model tries to combine the benefits of both prototyping and the waterfall model. • The basic idea is that the software should be developed in increments, where each increment adds some functional capability to the system until the full system is implemented. • At each step extensions and design modifications can be made. • The increments provide feedback to the client which is useful for determining the final requirements of the system.

11. Design0 Design1 Designn Implement0 Implement1 Implementn Analysis0 Analysis1 Analysisn Three phases of Iterative enhancement model

12. In the first step of iterative enhancement model, a simple initial implementation is done for a subset of the overall problem. This subset is the one that contains some of the key aspects of the problem. • A project control list is created which contains, in an order, all the tasks that must be performed to obtain the final implementation. • Each step consists of removing the next step from the list, designing the implementation for the selected task, coding and testing the implementation, and performing an analysis of the partial system obtained after this step and updating the list as a result of the analysis.

13. The process is iterated until the project control list is empty, at the time the final implementation of the system will be available.

14. Advantages:- • It combines benefits of both prototyping and waterfall model. • It can result in better testing because testing each increment is easier than testing entire system as a whole. • It can be used for product development in which developer themselves provide the specification.

15. Dis-advantages:- • Difficult to remove defect at later stage. • Early increments are less effective.

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