Incremental Process Model | Second type of prescriptive Process Model In software Engineering

In this model, the initial model with limited functionality is created for user's understanding about the software product and the this model is refined and expanded in later releases.

Incremental Model: 

• The incremental model has same phase that are in water model. But it is iterative in nature. The incremental model has following phases.

1. Analysis
2. Design
3. Code
4. Test

• The incremental model delivers series of releases to the customer. These releases are called increments. More and more functionality is associated with each increment.
• The first increment is called core product. In this release the basic requirements are implemented and then in subsequent increments new requirements are added.
•  The word processing software package can be considered as an example of incremental model.In the first increment only the document processing facilities are available. In the second increment, more sophisticated document producing and processing facilities, file management functionalities are given. In the next increment spelling and grammar checking facilities can be given. Thus in incremental model progressive functionalities are obtained with each release.

When to choose it?

1. When requirements are reasonably well-defined.
2. When overall scope of the development effort suggests a purely linear effort. 
3. When limited set of software functionality needed quickly.

 Merits of incremental model

1. The incremental model can be adopted when there are less number of people involved in the project.
2. Technical risks can be managed with each increment.
3. For a very small time, at least core product can be delivered to the customer.

RAD Model - Rapid Application Development Model

• The Rapid Application Development Model is a type of incremental process model in which there is extremely short development cycle.
• When the requirements are fully understood and the component based construction approach is adopted then the RAD Model is used.
• Using the Rapid Application Development Model the fully functional system can be developed with in 60 to 90 days. 
• Various  phases in RAD are Requirements Gathering, Analysis and Planning, Design, Build or Construction and finally Deployment.
• Multiple teams work on developing the software system using RAD model.
• In the requirements gathering phase the developers communicate with the users of the system and understand the business process and requirements of the software system.
• During analysis and planning phase, the analysis on the gathered requirements is made and a planning for various software development activities is done.
• During the design phase various model are created.Those models are business model, data model and process model.
• The build is an activity in which using the existing software components and automatic code generation tool the implementation code is created for the software system. This code is well tested by its team. The functionalities developed by all the teams are integrated to form a whole.
• Finally the deployment of all the software components that is created by various teams working on the project is carried out.

Drawbacks of Rapid Application Development

1. It requires Multiple team or large number of people to work on the projects.
2. This model requires heavily committed developer and customers. If commitment is lacking then RAD projects will fail.
3. The projects using RAD Model requires heavy resources.
4. If there is no appropriate modular then RAD projects fail. Performance can be problem to such project.
5. The projects using RAD model find it difficult to adopt new technologies.

Which type of applications suit RAD model?

• Solution: The RAD model is suitable for information system applications, business applications and the for systems that can be modular because of following reasons.

1. This model is similar to waterfall model but it uses very short development cycle.
2. It uses component based construction and code generation.
3. This model uses multiple teams on scale able projects.
4. The RAD model is suitable for the projects where technical risks are not high.
5. The RAD model requires heavy resources.

Examples

• There are various examples of software projects that would be amenable to incremental model.For instance

1. Banking software service: This service can be developed and distributed.This is the basic increment of the application. In the later increments the plugins can be provided to enhance the experience of web browser application.
2. Web browser application: The base application can be developed and distributed.This is the basic increment of the application. In the later increments the plugins can be provided to enhance the experience of web browser applications.
3. Operating system software: The operating system software providing the basic system handling functionalities is the first increment. After the release of the basic versions then updates or security patches are provided to the customer in the form of increments. Various distribution package in the form of versions such as basic home edition, premium, ultimate and so on can be the increments of operating system software.