Linear sequential model or be known as waterfall model is one of the approaches in Software Development Process Models that software engineer used to defined and design which are used during the development process of software. Parekh (n.d.) clearly stated that all these phases are cascaded to each other so that second phase is started as and when defined set of goals are achieved for first phase and it is signed off.
Phases of Linear Sequential Model (Startvbdotnet Contributor, n.d.)
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.
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.
Project Output in a Waterfall Model
As Freetutes.com Contributors (n.d.) has seen, the output of a project employing the waterfall model is not just the final program along with documentation to use it. There are a number of intermediate outputs, which must be produced in order to produce a successful product.
The set of documents that should be produced in each project are:
- Requirement document
- Project plan
- System design document
- Detailed design document
- Test plan and test report
- Final code
- Software manuals (user manual, installation manual etc.)
In order to certify an output product of a phase before the next phase begins, reviews are often held. Reviews are necessary especially for the requirements and design phases, since other certification means are frequently not available. Reviews are formal meeting to uncover deficiencies in a product. The review reports are the outcome of these reviews.
Based on the information given by The Software Tester Contributor (n.d.), below are the advantages and disadvantages for Linear Sequential Model.
Advantages of Linear Sequential Model
- Emphasizes requirements before design.
- Single system design phase emphasizes planning and design of the system architecture and technology before coding begins.
- Milestone reviews encourage close scrutiny of phase exit and entry criteria.
- Sequential progression through phases readily maps to configuration control points and the establishment of baselines.
- Model structure is readily understood and communicable to all stakeholders.
Disadvantages of Linear Sequential Model
- Testing does not receive focus until after the system has been specified, designed and coded.
- Many different units and sub-systems could be developed within the one project and the Waterfall Model implies that these are all specified and designed in one clump which does not reflect the reality
- Customer involvement is not throughout so issues with requirements are not always realized until later in the lifecycle.
- Linear progression through the phases can result in issue identification being pushed downstream resulting in many cycles of rework causing delays.
- The customer does not get to see the software until the very end.
- Project managers cannot always get a true picture of project health and progress, especially in the earlier phases.