Explain about spiral model

5. Explain about spiral model? 

Spiral Model - A New Approach Towards Software Development

The Waterfall model is the most simple and widely accepted/followed software development model, but like any other system, Waterfall model does have its own pros and cons. Spiral Model for software development  was designed in order to overcome the disadvantages of the Waterfall Model.

we discussed about "Waterfall Model", which is one of the oldest and most simple model designed and followed during software development process. But "Waterfall Model" has its own disadvantages such as there is no fair division of phases in the life cycle, not all the errors/problems related to a phase are resolved during the same phase, instead all those problems related to one phase are carried out in the next phase and are needed to be resolved in the next phase, this takes much of time of the next phase to solve them. The risk factor is the most important part, which affects the success rate of the software developed by following "The Waterfall Model".

In order to overcome the cons of "The Waterfall Model", it was necessary to develop a new Software Development Model, which could help in ensuring the success of software project. One such model was developed which incorporated the common methodologies followed in "The Waterfall Model", but it also eliminated almost every possible/known risk factors from it. This model is referred as "The Spiral Model" or "Boehm’s Model".

There are four phases in the "Spiral Model" which are: Planning, Evaluation, Risk Analysis and Engineering. These four phases are iteratively followed one after other in order to eliminate all the problems, which were faced in "The Waterfall Model". Iterating the phases helps in understating the problems associated with a phase and dealing with those problems when the same phase is repeated next time, planning and developing strategies to be followed while iterating through the phases. The phases in "Spiral Model" are:

Plan: In this phase, the objectives, alternatives and constraints of the project are determined and are documented. The objectives and other specifications are fixed in order to decide which strategies/approaches to follow during the project life cycle.

Risk Analysis: This phase is the most important part of "Spiral Model". In this phase all possible (and available) alternatives, which can help in developing a cost effective project are analyzed and strategies are decided to use them. This phase has been added specially in order to identify and resolve all the possible risks in the project development. If risks indicate any kind of uncertainty in requirements, prototyping may be  used to proceed with the available data and find out possible solution in order to deal with the potential changes in the requirements.

Engineering: In this phase, the actual development of the project is carried out. The output of this phase is passed through all the phases iteratively in order to obtain improvements in the same.

Customer Evaluation: In this phase, developed product is passed on to the customer in order to receive customer’s comments and suggestions which can help in identifying and resolving potential problems/errors in the software developed. This phase is very much similar to TESTING phase.

The process progresses in spiral sense to indicate iterative path followed, progressively more complete software is built as we go on iterating through all four phases. The first iteration in this model is considered to be most important, as in the first iteration almost all possible risk factors, constraints, requirements are identified and in the next iterations all known strategies are used to bring up a complete software system. The radical dimensions indicate evolution of the product towards a complete system.

However, as every system has its own pros and cons, "The Spiral Model" does have its pros and cons too. As this model is developed to overcome the disadvantages of the "Waterfall Model", to follow "Spiral Model", highly skilled people in the area of planning, risk analysis and mitigation, development, customer relation etc. are required. This along with the fact that the process needs to be iterated more than once demands more time and is somehow expensive task.

Six major activities of each designing spirals are represented by six major tasks:
1. Customer Communication
2. Planning
3. Risk Analysis
4. Software Designing Engineering
5. Construction and Release
6. Customer Evolution

Advantages

1. It facilities high amount of risk analysis.
2. This software designing model is more suitable for designing and managing large software projects.
3. The software is produced early in the software life cycle.

Disadvantages

1. Risk analysis requires high expertise.
2. It is costly model to use
3. Not suitable for smaller projects.
4. There is a lack of explicit process guidance in determining objectives, constraints and alternatives..
5. This model is relatively new. It does not have many practioners unlike the waterfall model or prototyping model.

                                                         1.22          Prototype model

1.22          Explain about Prototype model

/* In development the web based Applications before we start coding we develop a prototype and deliver a prototype to client or customer.

What is Prototype?

Ans:  Prototype is a dummy project developed by HTML Developers to get the approval of customer. Once the customer has approved the project prototype based on the project prototype we develop the code. Our Team Lead or project manager is the responisible to give the prototype to the developer. In the real time projects we develop the java code based on the Prototypes given by the Team Leads.  */

Prototyping is a technique that provides a reduced functionality or limited performance version of the eventual software to be delivered to the user in the early stages of the software development process. If used judiciously, this approach helps to solidify user requirements earlier, thereby making the waterfall approach more effective.
What is done is that before proceeding with design and coding, a throw away prototype is built to give user a feel of the system. The development of the software prototype also involves design and coding, but this is not done in a formal manner. The user interacts with the prototype as he would do with the eventual system and would therefore be in a better position to specify his requirements in a more detailed manner. The iterations occur to refine the prototype to satisfy the needs of the user, while at the same time enabling the developer to better understand what needs to be done.

Disadvantages

1. In prototyping, as the prototype has to be discarded, so might argue that the cost involved is higher.
2. At times, while designing a prototype, the approach adopted is “quick and dirty” with the focus on quick development rather than quality.
3. The developer often makes implementation compromises in order to get a prototype working quickly.

1.23          Evolutinary model

Evolutionary prototyping model

Evolutionary prototyping model is a software development lifecycle model in which software prototype created for demonstration and requirements elaboration. Evolutionary prototyping model includes the four main phases:

Definition the basic requirements

Creating the working prototype

Verification of the working prototype

Changing or elaboration the requirements

Evolutionary prototyping model allows create working software prototypes fast and may be applicable to projects where:

System requirements early are not known in advance

Creating fundamentally new software