Software Engineering Lecture 18

Rapid Prototyping Model Requirement Definition System and Software Design Implementation and Unit Testing Integration and System Testing Operation and Maintenance Rapid Prototyping Real projects rarely follow the sequential flow that the model proposes. In general these phases overlap and feed information to each other. Hence there should be an element of iteration and feedback. A mistake caught any stage should be referred back to the source and all the subsequent stages need to be revisited and corresponding documents should be updated accordingly. Because of the costs of producing and approving documents, iterations are costly and require significant rework.

Incremental Model the product is partitioned into smaller pieces which are then built and delivered to the client in increments at regular intervals. Since each piece is much smaller than the whole, it can be built and sent to the client quickly. This results in quick feedback from the client and any requirement related errors or changes can be incorporated at a much lesser cost. As discussed above, the major drawbacks of the waterfall model are due to the fact that the entire product is developed and delivered to the client in one package. This results in delayed feedback from the client. Because of the long elapsed time, a huge new investment of time and money may be required to fix any errors of omission or commission or to accommodate any new requirements cropping up during this period. This may render the product as unusable. Incremental model may be used to overcome these issues. In a more risky version, once the user requirements have been elicited, the specifications of the first build are drawn up. When this has been completed, the specification team turns to the specification of the second build while the design team designs the first build. Thus the various builds are constructed in parallel, with each team making use of the information gained in the all the previous builds. This approach incurs the risk that the resulting build will not fit together and hence requires careful monitoring.

Incremental Model Requirements phase Verify Specification phase Verify Architectural design Verify For each build: Perform detailed design, implementation and integration, test, deliver to client Maintenance phase Development Maintenance Retirement

Incremental Model (cont.) Build 1 Implementation, integration Deliver to client Design Specification Implementation, integration Deliver to client Design Specification Build 2 Build 3 Implementation, integration Deliver to client Design Specification Build n Implementation, integration Deliver to client Design Specification Specification team Implementation, integration team Design team

Synchronize and Stabilize Model The requirements analysis interviews of potential customers are conducted and requirements document is developed. Once these requirements have been captured, specifications are drawn up. The project is then divided into 3 or 4 builds. Each build is carried out by small teams working in parallel. At the end of each day the code is synchronized (test and debug) and at the end of the build it is stabilized by freezing the build and removing any remaining defects. Because of the synchronizations, components always work together. The presence of an executable provides early insights into operation of product.

Rapid Application Development (RAD) Rapid application development is another form of incremental model. It is a high speed adaptation of the linear sequential model in which fully functional system in a very short time (2-3 months). This model is only applicable in the projects where requirements are well understood and project scope is constrained. Because of this reason it is used primarily for information systems.