SDLC Overview

SDLC, Software Development Life Cycle is a process used by software industry to design, develop and test high quality software. The SDLC aims to produce high quality software that meets or exceeds customer expectations, reaches completion within times and cost estimates.

A typical Software Development life cycle consists of the following stages:

Stage 1: Planning and Requirement Analysis

Stage 2: Defining Requirements

Stage 3: Designing the product architecture

Stage 4: Building or Developing the Product

Stage 5: Testing the Product

Stage 6: Deployment in the Market and Maintenance

SDLC Models

There are various software development life cycle models defined and designed which are followed during software development process. These models are also referred as "Software Development Process Models". Each process model follows a Series of steps unique to its type, in order to ensure success in process of software development.

Following are the most important and popular SDLC models followed in the industry:

·      Waterfall Model

·      Iterative Model

·      Spiral Model

·      V-Model

·      Big Bang Model

The other related methodologies are Agile Model, RAD Model, Rapid Application Development and Prototyping Models.

SDLC Waterfall Model

Following is a diagrammatic representation of different phases of 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 doc.

·     System Design: The requirement specifications from first phase are studied in this phase and system design is prepared. System Design helps in specifying hardware and system requirements and also helps in defining overall system architecture.

·      Implementation: With inputs from 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.

All these phases are cascaded to each other in which progress is seen as flowing steadily downwards (like a waterfall) through the phases. The next phase is started only after the defined set of goals are achieved for previous phase and it is signed off, so the name "Waterfall Model". In this model phases do not overlap.

Pros	Cons
·       Simple and easy to understand and use	·       No working software is produced until late during the life cycle.
·       Easy to manage due to the rigidity of the model. each phase has specific deliverables and a review process.	·       High amounts of risk and uncertainty.
·       Phases are processed and completed one at a time.	·       Not a good model for complex and object-oriented projects.
·       Works well for smaller projects where requirements are very well understood.	·       Poor model for long and ongoing projects.
·       Clearly defined stages.	·       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.
·       Well understood milestones.	·       It is difficult to measure progress within stages.
·       Easy to arrange tasks.	·       Cannot accommodate changing requirements.
·       Process and results are well documented.	·       No working software is produced until late in the life cycle.
	·       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.

Spiral Model

Pros	Cons
Changing requirements can be accommodated.	Management is more complex.
Allows for extensive use of prototypes	End of project may not be known early.
Requirements can be captured more accurately.	Not suitable for small or low risk projects and could be expensive for small projects.
Users see the system early.	Process is complex
Development can be divided into smaller parts and more risky parts can be developed earlier which helps better risk management.	Spiral may go indefinitely.
	Large number of intermediate stages requires excessive documentation.

V- Model design

Under V-Model, the corresponding testing phase of the development phase is planned in parallel. So there are Verification phases on one side of the .V. and Validation phases on the other side. Coding phase joins the two sides of the V-Model.

The below figure illustrates the different phases in V-Model of SDLC.

Verification Phases

Following are the Verification phases in V-Model:

·     Business Requirement Analysis: This is the first phase in the development cycle where the product requirements are understood from the customer perspective. This phase involves detailed communication with the customer to understand his expectations and exact requirement. This is a very important activity and need to be managed well, as most of the customers are not sure about what exactly they need. The acceptance test design planning is done at this stage as business requirements can be used as an input for acceptance testing.

·       System Design: Once you have the clear and detailed product requirements, it.s time to design the complete system. System design would comprise of understanding and detailing the complete hardware and communication setup for the product under development. System test plan is developed based on the system design. Doing this at an earlier stage leaves more time for actual test execution later.

·       Architectural Design: Architectural specifications are understood and designed in this phase. Usually more than one technical approach is proposed and based on the technical and financial feasibility the final decision is taken. System design is broken down further into modules taking up different functionality. This is also referred to as High Level Design (HLD).

The data transfer and communication between the internal modules and with the outside world (other systems) is clearly understood and defined in this stage. With this information, integration tests can be designed and documented during this stage.

·       Module Design: In this phase the detailed internal design for all the system modules is specified, referred to as Low Level Design (LLD). It is important that the design is compatible with the other modules in the system architecture and the other external systems. Unit tests are an essential part of any development process and helps eliminate the maximum faults and errors at a very early stage. Unit tests can be designed at this stage based on the internal module designs.

Coding Phase

The actual coding of the system modules designed in the design phase is taken up in the Coding phase. The best suitable programming language is decided based on the system and architectural requirements. The coding is performed based on the coding guidelines and standards. The code goes through numerous code reviews and is optimized for best performance before the final build is checked into the repository.

Validation Phases

Following are the Validation phases in V-Model:

·       Unit Testing: Unit tests designed in the module design phase are executed on the code during this validation phase. Unit testing is the testing at code level and helps eliminate bugs at an early stage, though all defects cannot be uncovered by unit testing.

·    Integration Testing: Integration testing is associated with the architectural design phase. Integration tests are performed to test the coexistence and communication of the internal modules within the system.

·       System Testing: System testing is directly associated with the System design phase. System tests check the entire system functionality and the communication of the system under development with external systems. Most of the software and hardware compatibility issues can be uncovered during system test execution.

·       Acceptance Testing: Acceptance testing is associated with the business requirement analysis phase and involves testing the product in user environment. Acceptance tests uncover the compatibility issues with the other systems available in the user environment. It also discovers the non functional issues such as load and performance defects in the actual user environment.

V- Model Application

V- Model application is almost same as waterfall model, as both the models are of sequential type. Requirements have to be very clear before the project starts, because it is usually expensive to go back and make changes. This model is used in the medical development field, as it is strictly disciplined domain. Following are the suitable scenarios to use V-Model:

·       Requirements are well defined, clearly documented and fixed.

·       Product definition is stable.

·       Technology is not dynamic and is well understood by the project team.

·       There are no ambiguous or undefined requirements.

·       The project is short.

V- Model Pros and Cons

The advantage of V-Model is that it.s very easy to understand and apply. The simplicity of this model also makes it easier to manage. The disadvantage is that the model is not flexible to changes and just in case there is a requirement change, which is very common in today.s dynamic world, it becomes very expensive to make the change.