SDLC

Systems Development Life Cycle

The systems development life cycle (SDLC), also referred to as the application/software development life-cycle, is a term used in systems engineering, information systems and software engineering to describe a process for planning, creating, testing, and deploying an information system.[1] The systems development lifecycle concept applies to a range of hardware and software configurations, as a system can be composed of hardware only, software only, or a combination of both.
SDLC can be described along a spectrum of agile to iterative to sequential methodologies. Agile methodologies, such as XP and Scrum, focus on lightweight processes which allow for rapid changes (without necessarily following the pattern of SDLC approach) along the development cycle. Iterative methodologies, such as Rational Unified Process and dynamic systems development method, focus on limited project scope and expanding or improving products by multiple iterations. Sequential or big-design-up-front (BDUF) models, such as waterfall, focus on complete and correct planning to guide large projects and risks to successful and predictable results.[citation needed] Other models, such as anamorphic development, tend to focus on a form of development that is guided by project scope and adaptive iterations of feature development.
In project management a project can be defined both with a project life cycle (PLC) and an SDLC, during which slightly different activities occur. According to Taylor (2004), "the project life cycle encompasses all the activities of the project, while the systems development life cycle focuses on realizing the product requirements".
SDLC is used during the development of an IT project, it describes the different stages involved in the project from the drawing board, through the completion of the project.
The following figure is a graphical representation of the various stages of a typical SDLC.


A typical Software Development Life Cycle consists of the following stages;
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. The outcome of the technical feasibility study is to define the various technical approaches that can be followed to implement the project successfully with minimum risks.
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 refere.nce for product architects to come out with the best architecture for the product to be developed. Based on the requirements specified in S,brRS, usually more than one design approach for the product architecture is proposed and documented in a DDS - Design Document Specification.
This DDS is reviewed by all the important stakeholders and based on various parameters as risk assessment, product robustness, design modularity, budget and time constraints, the best design approach is selected for the product.
A design approach clearly defines all the architectural modules of the product along with its communication and data flow representation with the external and third party modules (if any). The internal design of all the modules of the proposed architecture should be clearly defined with the minutest of the details in DDS.
Stage-4: Building or Developing a 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.
Developers must follow the coding guidelines defined by their organization and programming tools like compilers, interpreters, debuggers, etc. are used to generate the code. Different high level programming languages such as C, C++, Pascal, Java and PHP are used for coding. The programming language is chosen with respect to the type of software being developed.
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.

There are various types of software development models used in industry such as,

• Waterfall Model.
• Iterative Model.
• Spiral Model.
• V-Model.
• Big Bang Model.

Other related methodologies are Agile Model, RAD Model, Rapid Application Development and Prototyping Models.
Out of the above mentioned models we would focus on two major models used today i.e.,

• Waterfall Model.
• Agile Model.

• Waterfall Model.

The Waterfall Model was the first Process Model to be introduced. It is also referred to as a linear-sequential life cycle model. It is very simple to understand and use. In a waterfall model, each phase must be completed before the next phase can begin and there is no overlapping in the phases.
The Waterfall model is the earliest SDLC approach that was used for software development.
The waterfall Model illustrates the software development process in a linear sequential flow. This means that any phase in the development process begins only if the previous phase is complete. In this waterfall model, the phases do not overlap.
The following illustration is a representation of the different phases of the Waterfall Model.


The sequential phases in Waterfall model are,

• Requirement Gathering and analysis

All possible requirements of the system to be developed are captured in this phase and documented in a requirement specification document.

• System Design

The requirement specifications from first phase are studied in this phase and the system design is prepared. This system design helps in specifying hardware and system requirements and helps in defining the overall system architecture.

• Implementation

With inputs from the system design, the system is first developed in small programs called units, which are integrated in the next phase. Each unit is developed and tested for its functionality, which is referred to as Unit Testing.

• Integration and Testing

All the units developed in the implementation phase are integrated into a system after testing of each unit. Post integration the entire system is tested for any faults and failures.

• Deployment of system

Once the functional and non-functional testing is done; the product is deployed in the customer environment or released into the market.

• Maintenance

There are some issues which come up in the client environment. To fix those issues, patches are released. Also to enhance the product some better versions are released. Maintenance is done to deliver these changes in the customer environment.



Waterfall Model Application
Some situations where the use of Waterfall model is most appropriate are −

• Requirements are very well documented, clear and fixed.
• Product definition is stable.
• Technology is understood and is not dynamic.
• There are no ambiguous requirements.
• Ample resources with required expertise are available to support the product.
• The project is short.


Waterfall 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.


Waterfall Model - 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.



• Agile Model:

Agile SDLC model is a combination of iterative and incremental process models with focus on process adaptability and customer satisfaction by rapid delivery of working software product. Agile Methods break the product into small incremental builds. These builds are provided in iterations. Each iteration typically lasts from about one to three weeks.
Every iteration involves cross functional teams working simultaneously on various areas like;

• Planning.
• Requirements Analysis.
• Design.
• Coding.
• Unit Testing.
• Acceptance Testing.
At the end of the iteration, a working product is displayed to the customer and important stakeholders.
What is Agile ?
Agile model believes that every project needs to be handled differently and the existing methods need to be tailored to best suit the project requirements. In Agile, the tasks are divided to time boxes (small time frames) to deliver specific features for a release.
Iterative approach is taken and working software build is delivered after each iteration. Each build is incremental in terms of features; the final build holds all the features required by the customer.

The Agile thought process had started early in the software development and started becoming popular with time due to its flexibility and adaptability.
The most popular Agile methods include Rational Unified Process (1994), Scrum (1995), Crystal Clear, Extreme Programming (1996), Adaptive Software Development, Feature Driven Development, and Dynamic Systems Development Method (DSDM) (1995). These are now collectively referred to as Agile Methodologies, after the Agile Manifesto was published in 2001.
Following are the Agile Manifesto principles;

• Individuals and interactions

In Agile development, self-organization and motivation are important, as are interactions like co-location and pair programming.

• Working software

Demo working software is considered the best means of communication with the customers to understand their requirements, instead of just depending on documentation.

• Customer collaboration

As the requirements cannot be gathered completely in the beginning of the project due to various factors, continuous customer interaction is very important to get proper product requirements.

• Responding to change

Agile Development is focused on quick responses to change and continuous development.


Agile Model - Pros and Cons
The advantages of the Agile Model are as follows −
• 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.

The disadvantages of the Agile Model are as follows;

• 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.

Web references;
Waterfall Model
Agile Model
SDLC-Overview
Wikipedia