The Systems Life Cycle and the Waterfall Model
Introduction - what is a 'Systems Life Cycle'?
The phrase ‘Systems Life Cycle’ simply describes the steps that are taken in a project, from the time that the project is started to when it is finished. When any computer-related project is initiated, a number of distinct steps, or stages, can be identified in the life of the project. Each of these stages will involve people doing jobs and producing 'things', for example, a design document, a test plan or a piece of program code. Each of these things takes the project a little further towards completion. Things that have to be produced for each stage are known as ‘deliverables’, for example, a report.
The idea behind the Systems Life Cycle is that the deliverables associated with each stage in the project must be produced and checked off by the Project Manager before the next stage can begin. A stage cannot be started until the previous stage is finished. This stops a project getting ahead of itself. For example, it will stop someone trying to start the stage called 'implementation' (the stage where you actually make the project using a database application or code) before all of the design documentation has been completed. You may have had some experience of this scenario yourselves with coursework - you don't want to do the paperwork or a detailed design, you just want to get on and do the project! This, however, is the road to potential disaster! For example:
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- How can a project be designed if it is not clear what the problem is?
- How can a project be built if it is not designed?
- How can it be installed if it is not properly tested?
- What happens if a key project member leaves - how can someone new pick up where they left off if half of the paperwork is missing or incomplete?
- How can a Project Manager accurately manage a project if they can't clearly see that deliverables are being completed on time and within the budget?
- How can someone make changes to the product in the future if the documentation is incomplete?
The Waterfall Model
The list of potential problems goes on and on. A Systems Life Cycle gives a project a structure and therefore allows a Project Manager to manage the project rather than reacting to things when they go wrong! There are a number of models for a project management structure. One of the most common models is known as the 'Waterfall Model'. In this model, a project has a set of identifiable stages. In each stage, there is a set of activities that must happen in a certain order, and a set of outcomes (called 'deliverables') that must be produced and signed off as completed by the Project Manager for each stage before the next one is started. The stages can be summarised below.
Waterfall
Notice with this model that there is nothing stopping a stage feeding back into an earlier stage, so that the project can constantly loop around until it is perfect! You should also be aware that different sources sometimes give the stages different names, or include extra stages or don't include some of the ones above. There is no 'definitive' version of what the Waterfall Model should look like although as always, we have followed the model as laid down and described in the British Computing Society's Glossary.