Software Development Life Cycle and Methodologies.

SDLC is a process followed for a software project, within a software organization. It consists of a detailed plan describing how to develop, maintain, replace and alter or enhance specific software. The life cycle defines a methodology for improving the quality of software and the overall development process.

Stage 1: Planning and Requirement Analysis

Requirement analysis is the most important and fundamental stage in SDLC. It is performed by the senior members of the team with inputs from the customer, the sales department, market surveys and domain experts in the industry. This information is then used to plan the basic project approach and to conduct product feasibility study in the economical, operational and technical areas. Planning for the quality assurance requirements and identification of the risks associated with the project is also done in the planning stage.

Stage 2: Defining Requirements

Once the requirement analysis is done the next step is to clearly define and document the product requirements and get them approved from the customer or the market analysts. This is done through an SRS (Software Requirement Specification) document which consists of all the product requirements to be designed and developed during the project life cycle.

Stage 3: Designing the Product Architecture

SRS is the reference for product architects to come out with the best architecture for the product to be developed. Based on the requirements specified in SRS, usually more than one design approach for the product architecture is proposed and documented in a DDS — Design Document Specification.

Stage 4: Building or Developing the Product

In this stage of SDLC the actual development starts and the product is built. The programming code is generated as per DDS during this stage. If the design is performed in a detailed and organized manner, code generation can be accomplished without much hassle.

Stage 5: Testing the Product

This stage is usually a subset of all the stages as in the modern SDLC models, the testing activities are mostly involved in all the stages of SDLC. However, this stage refers to the testing only stage of the product where product defects are reported, tracked, fixed and retested, until the product reaches the quality standards defined in the SRS.

Stage 6: Deployment in the Market and Maintenance

Once the product is tested and ready to be deployed it is released formally in the appropriate market. Sometimes product deployment happens in stages as per the business strategy of that organization. The product may first be released in a limited segment and tested in the real business environment (UAT- User acceptance testing). Then based on the feedback, the product may be released as it is or with suggested enhancements in the targeting market segment. After the product is released in the market, its maintenance is done for the existing customer base.

SDLC Models

1. Waterfall SDLC Model

Waterfall-is a cascade SDLC model, in which development process looks like the flow, moving step by step through the phases of analysis, projecting, realization, testing, implementation, and support. This SDLC model includes gradual execution of every stage completely. This process is strictly documented and predefined with features expected to every phase of this software development life cycle model.

Advantages

• Simple and easy to understand and use
• Easy to manage due to the rigidity of the model. Each phase has specific deliverables and a review process.
• Phases are processed and completed one at a time.
• Works well for smaller projects where requirements are very well understood.
• Clearly defined stages.
• Well understood milestones.
• Easy to arrange tasks.
• Process and results are well documented.

Disadvantages

• No working software is produced until late during the life cycle.
• High amounts of risk and uncertainty.
• Not a good model for complex and object-oriented projects.
• Poor model for long and ongoing projects.
• Not suitable for the projects where requirements are at a moderate to high risk of changing. So, risk and uncertainty is high with this process model.
• It is difficult to measure progress within stages.
• Cannot accommodate changing requirements.
• Adjusting scope during the life cycle can end a project.
• Integration is done as a “big-bang. at the very end, which doesn’t allow identifying any technological or business bottleneck or challenges early.

2.V-shaped SDLC Model

V-shaped SDLC model is an expansion of classic waterfall model and it’s based on associated test stage for the every development stage. This is a very strict model and the next stage is started only after the previous phase. This is also called “Validation and verification” model. Every stage has the current process control, to make sure that the conversion to the next stage is possible.

Advantages

• This is a highly-disciplined model and Phases are completed one at a time.
• Works well for smaller projects where requirements are very well understood.
• Simple and easy to understand and use.
• Easy to manage due to the rigidity of the model. Each phase has specific deliverables and a review process.

Disadvantages

• High risk and uncertainty.
• Not a good model for complex and object-oriented projects.
• Poor model for long and ongoing projects.
• Not suitable for the projects where requirements are at a moderate to high risk of changing.
• Once an application is in the testing stage, it is difficult to go back and change a functionality.
• No working software is produced until late during the life cycle.

3.Spiral SDLC Model

Spiral model-is SDLC model, which combines architecture and prototyping by stages. It is a combination of the Iterative and Waterfall SDLC models with the significant accent on the risk analysis. The main issue of the spiral model-is defining the right moment to make a step into the next stage. The preliminary set time frames are recommended as the solution to this issue. The shift to the next stage is done according to the plan, even if the work on the previous stage isn’t done yet. The plan is introduced basing on the statistic data, received during the previous projects even from the personal developer’s experience.

Advantages

• Changing requirements can be accommodated.
• Allows extensive use of prototypes.
• Requirements can be captured more accurately.
• Users see the system early.
• Development can be divided into smaller parts and the risky parts can be developed earlier which helps in better risk management.

Disadvantages

• Management is more complex.
• End of the project may not be known early.
• Not suitable for small or low risk projects and could be expensive for small projects.
• Process is complex
• Spiral may go on indefinitely.
• Large number of intermediate stages requires excessive documentation.

4.Agile SDLC Model

In the agile methodology after every development iteration, the customer is able to see the result and understand if he is satisfied with it or he is not. This is one of the advantages of the agile software development life cycle model. One of its disadvantages is that with the absence of defined requirements it is difficult to estimate the resources and development cost. Extreme programming is one of the practical use of the agile model. The basis of such model consists of short weekly meetings-Sprints which are the part of the Scrum approach.

Advantages

• Is a very realistic approach to software development.
• Promotes teamwork and cross training.
• Functionality can be developed rapidly and demonstrated.
• Resource requirements are minimum.
• Suitable for fixed or changing requirements
• Delivers early partial working solutions.
• Good model for environments that change steadily.
• Minimal rules, documentation easily employed.
• Enables concurrent development and delivery within an overall planned context.
• Little or no planning required.
• Easy to manage.
• Gives flexibility to developers.

Disadvantages

• Not suitable for handling complex dependencies.
• More risk of sustainability, maintainability and extensibility.
• An overall plan, an agile leader and agile PM practice is a must without which it will not work.
• Strict delivery management dictates the scope, functionality to be delivered, and adjustments to meet the deadlines.
• Depends heavily on customer interaction, so if customer is not clear, team can be driven in the wrong direction.
• There is a very high individual dependency, since there is minimum documentation generated.
• Transfer of technology to new team members may be quite challenging due to lack of documentation.

5.Iterative Model

In the Iterative model, iterative process starts with a simple implementation of a small set of the software requirements and iteratively enhances the evolving versions until the complete system is implemented and ready to be deployed.

An iterative life cycle model does not attempt to start with a full specification of requirements. Instead, development begins by specifying and implementing just part of the software, which is then reviewed to identify further requirements. This process is then repeated, producing a new version of the software at the end of each iteration of the model.

Advantages

• Some working functionality can be developed quickly and early in the life cycle.
• Results are obtained early and periodically.
• Parallel development can be planned.
• Progress can be measured.
• Less costly to change the scope/requirements.
• Testing and debugging during smaller iteration is easy.
• Risks are identified and resolved during iteration; and each iteration is an easily managed milestone.
• Easier to manage risk -High risk part is done first.
• With every increment, operational product is delivered.
• Issues, challenges and risks identified from each increment can be utilized/applied to the next increment.
• Risk analysis is better.
• It supports changing requirements.
• Initial Operating time is less.
• Better suited for large and mission-critical projects.
• During the life cycle, software is produced early which facilitates customer evaluation and feedback.

Disadvantages

• More resources may be required.
• Although cost of change is lesser, but it is not very suitable for changing requirements.
• More management attention is required.
• System architecture or design issues may arise because not all requirements are gathered in the beginning of the entire life cycle.
• Defining increments may require definition of the complete system.
• Not suitable for smaller projects.
• Management complexity is more.
• End of project may not be known which is a risk.
• Highly skilled resources are required for risk analysis.
• Projects progress is highly dependent upon the risk analysis phase.