Software Engineering | Rapid application development model (RAD)

The Rapid Application Development Model was first proposed by IBM in the 1980s. The RAD 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. Various phases in RAD are Requirements Gathering, Analysis and Planning, Design, Build or Construction, and finally Deployment.

The critical feature of this model is the use of powerful development tools and techniques. A software project can be implemented using this model if the project can be broken down into small modules wherein each module can be assigned independently to separate teams. These modules can finally be combined to form the final product. Development of each module involves the various basic steps as in the waterfall model i.e. analyzing, designing, coding, and then testing, etc. as shown in the figure. Another striking feature of this model is a short time span i.e. the time frame for delivery(time-box) is generally 60-90 days.

⚫ Multiple teams work on developing the software system using RAD model parallely. 

The use of powerful developer tools such as JAVA, C++, Visual BASIC, XML, etc. is also an integral part of the projects. This model consists of 4 basic phases:

1. Requirements Planning – It involves the use of various techniques used in requirements elicitation like brainstorming, task analysis, form analysis, user scenarios, FAST (Facilitated Application Development Technique), etc. It also consists of the entire structured plan describing the critical data, methods to obtain it, and then processing it to form a final refined model.
2. User Description – This phase consists of taking user feedback and building the prototype using developer tools. In other words, it includes re-examination and validation of the data collected in the first phase. The dataset attributes are also identified and elucidated in this phase.
3. Construction – In this phase, refinement of the prototype and delivery takes place. It includes the actual use of powerful automated tools to transform processes and data models into the final working product. All the required modifications and enhancements are too done in this phase.
4. Cutover – All the interfaces between the independent modules developed by separate teams have to be tested properly. The use of powerfully automated tools and subparts makes testing easier. This is followed by acceptance testing by the user.

The process involves building a rapid prototype, delivering it to the customer, and taking feedback. After validation by the customer, the SRS document is developed and the design is finalized. 

When to use RAD Model?

When the customer has well-known requirements, the user is involved throughout the life cycle, the project can be time-boxed, the functionality delivered in increments, high performance is not required, low technical risks are involved and the system can be modularized. In these cases, we can use the RAD Model. when it is necessary to design a system that can be divided into smaller units within two to three months. when there is enough money in the budget to pay for both the expense of automated tools for code creation and designers for modeling.

Advantages:

• The use of reusable components helps to reduce the cycle time of the project.
• Feedback from the customer is available at the initial stages.
• Reduced costs as fewer developers are required.
• The use of powerful development tools results in better quality products in comparatively shorter time spans.
• The progress and development of the project can be measured through the various stages.
• It is easier to accommodate changing requirements due to the short iteration time spans.
• Productivity may be quickly boosted with a lower number of employees.

Disadvantages:

• The use of powerful and efficient tools requires highly skilled professionals.
• The absence of reusable components can lead to the failure of the project.
• The team leader must work closely with the developers and customers to close the project on time.
• The systems which cannot be modularized suitably cannot use this model.
• Customer involvement is required throughout the life cycle.
• It is not meant for small-scale projects as in such cases, the cost of using automated tools and techniques may exceed the entire budget of the project.
• Not every application can be used with RAD.

Applications:

1. This model should be used for a system with known requirements and requiring a short development time.
2. It is also suitable for projects where requirements can be modularized and reusable components are also available for development.
3. The model can also be used when already existing system components can be used in developing a new system with minimum changes.
4. This model can only be used if the teams consist of domain experts. This is because relevant knowledge and the ability to use powerful techniques are a necessity.
5. The model should be chosen when the budget permits the use of automated tools and techniques required.

Drawbacks of rapid application development:

• It requires multiple teams or a large number of people to work on the scalable projects.
• This model requires heavily committed developer and customers. If commitment is lacking then RAD projects will fail.
• The projects using RAD model requires heavy resources.
• If there is no appropriate modularization then RAD projects fail. Performance can be problem to such projects.
• The projects using RAD model find it difficult to adopt new technologies.