Curtain Raiser
As in any other engineering disciplines, software engineering also has some structured models for software development. This document will provide you with a generic overview about different software development methodologies adopted by the contemporary software firms. Before we get into the of the different models, we shall have a brief insight about the basics that spread throughout these models.

Like any other engineering products, software products are oriented towards customers. It is either market driven (or) it drives the market. Customer Satisfaction was the buzzword of the 80’s. Customer Delight is today’s buzzword and Customer Ecstasy is the buzzword of the new millennium. Products that are not customer (user) friendly have no place in the market although they are engineered using the best technology. The interface of the product is as crucial as the internal technology of the product.

Market Research
Market study is made to identify the potential customers need. This process is also known as market research. In the market research, the already existing need and the possible/potential needs that are available in a segment of the society is studied carefully. The market study is done based on lot of assumptions. Assumptions are the crucial factors in the development or inception of a product development. Unrealistic assumptions can become a nosedive in the entire venture. Though assumptions are abstract, there should be a move to develop tangible assumptions to come up with a successful product.

Research and Development
Once the Market study is made, the customer’s need is given to the Research and Development (R&D) Department to conceptualize a cost-effective system that could potentially solve customer’s need better than the competitors. Once the conceptual system is developed and tested in a hypothetical environment, the development team takes control of it. The development team adopts one of the software development methodologies that is given below, develop the proposed system, and gives it to the customers.

The Marketing group starts selling the product to the available customers and simultaneously work in developing a niche segment that could potentially buy the product. In addition, the marketing group passes the feedback from the customers to the developers and the R&D group to make possible value additions in the product.

While developing a product, the company outsources** the non-core activities to the other companies who specialize in those activities. This accelerates the product development process largely. Some companies work on tie-ups to bring out highly matured product in a short period.

Following are the basic popular models used by many software development firms.

• System Development Life Cycle Model
• Prototyping Model
• Rapid Application Development Model
• Component Assembly Model

Let us watch one by one in the following chapters.

System Development Life Cycle Model
This is also known as Classic Life Cycle Model (or) Linear Sequential Model (or) Waterfall Method. This has the following activities.

1. System/Information Engineering and Modeling

2. Software Requirements Analysis

3. Systems Analysis and Design

4. Code Generation

5. Testing

6. Maintenance

System/Information Engineering and Modeling
As software is always of a large system (or business), work begins by establishing requirements for all system elements and then allocating some subset of these requirements to software. This system view is essential when software must interface with other elements such as hardware, people and other resources. System is the basic and very critical requirement for the existence of software in any entity. So if the system is not in place, the system should be engineered and put in place. In some cases to extract the maximum output, system should be re-engineered and spiced up. Once the ideal system is engineered or tuned up, the development team studies the software requirement for the system.

Software Requirements Analysis
This is also known as feasibility study. In this phase, the development team visits the customer and studies their system. They investigate the need for possible software automation in the given system. By the end of the feasibility study, the team furnishes a document that holds the different specific recommendations for the candidate system. It also includes the personnel assignments, costs, project schedule, and target dates. The requirements gathering process is intensified and focussed specially on software. To understand the nature of the program(s) to be built, the system engineer (“analyst”) must understand the information domain for the software, as well as required function, behavior, performance and interfacing. The essential purpose of this phase is to find the need and to define the problem that needs to be solved .

System Analysis and Design
In this phase, the software’s overall structure and its nuances are defined. In terms of the client/server technology, the number of tiers needed for the package architecture, the database design, the data structure design etc are all defined in this phase. Analysis and Design are very crucial in the whole development cycle. Any glitch in the design phase could be very expensive to solve in the later stage of the software development. Much care is taken during this phase. The logical system of the product is developed in this phase.

Code Generation
The design must be translated into a machine-readable form. The code generation step performs this task. If design is performed in a detailed manner, code generation can be accomplished with out much complication. Programming tools like Compilers, Interpreters, Debuggers are used to generate the code. Different high level programming languages like C, C++, Pascal, Java are used for coding. With respect to the type of application, the right programming language is chosen.

Testing
Once the code is generated, the program testing begins. Different testing methodologies are available to unravel the bugs that were committed during the previous phases. Different testing tools and methodologies are already available. Some companies built there own testing tools that are tailor made for there own development operations.

Maintenance
Software will definitely undergo change once it is delivered to the customer. There are many reasons for the change. Change could happen because of some unexpected input values into the system. In addition, the changes in the system could directly affect the software operations. The software should be developed to accommodate changes that could happen during the post implementation period.

Prototyping Model
This is a cyclic version of the linear model. In this model, once the requirement analysis is done and the design for a prototype is made, the development process gets started. Once the prototype is created, it is given to the customer for evaluation. The customer tests the package and gives his/her feed back to the developer who refines the product according to the customer’s exact expectation. After a finite number of iterations, the final software package is given to the customer. In this methodology, the software is evolved as a result of periodic shuttling of information between the customer and developer. This is the most popular development model in the contemporary IT industry. Most of the successful software products have been developed using this model – as it is very difficult (even for a whiz kid!) to comprehend all the requirements of a customer in one shot. There are many variations of this model skewed with respect to the project management styles of the companies. New versions of software product evolve as a result of prototyping.

Rapid Application Development (RAD) Model
The RAD is a linear sequential software development process that emphasizes an extremely short development cycle. The RAD model is a “high speed” adaptation of the linear sequential model in which rapid development is achieved by using a component-based construction approach. Used primarily for information systems applications, the RAD approach encompasses the following phases:

Business modeling
The information flow among business function is modeled in a way that answers the following questions:
What information drives the business process?
What information is generated?
Who generates it?
Where does the information go?
Who processes it?

Data modeling
The information flow defined as part of the business modeling phase is refined into a set of data objects that are needed to support the business. The characteristic (called attributes) of each object share identified and the relationships between these objects are defined.

Process modeling
The data objects defined in the data-modeling phase are transformed to achieve the information flow necessary to implement a business function. Processing the descriptions are created for adding, modifying, deleting, or retrieving a data object.

Application generation
RAD assumes the use of the RAD tools like VB, VC++, Delphi etc rather than creating software using conventional third generation programming languages. The RAD works to reuse existing program components (when possible) or create reusable components (when necessary). In all cases, automated tools are used to facilitate construction of the software.

Testing and turnover

Since the RAD process emphasizes reuse, many of the program components have already been tested. This minimizes the testing and development time.

Component Assembly Model
Object technologies provide the technical framework for a component-based process model for software engineering. The object oriented paradigm emphasizes the creation of classes that encapsulate both data and the algorithm that are used to manipulate the data. If properly designed and implemented, object oriented classes are reusable across different applications and computer based system architectures. Component Assembly Model leads to software reusability. The integration/assembly of the already existing software components accelerate the development process. Nowadays many component libraries are available in the Internet. If the right components are chosen, the integration aspect is made much simpler.

Conclusion
All these different models have their own advantages and disadvantages. Nevertheless, in the contemporary commercial software development world, the fusion of all these methodologies is incorporated. Timing is very crucial in software development. If a delay happens in the development phase, the market could be taken over by the competitor. Also if a ‘bug’ filled product is launched in a short period of time (quicker than the competitors), it may affect the reputation of the company. So, there should be a tradeoff between the development time and the quality of the product. Customers don’t expect a bug free product but they expect a user-friendly product. That results in Customer Ecstasy!