An introduction to SDLC - System Development Life Cycles.

An introduction to SDLC

System Development Life Cycles or SDLC’s have been with us since time began. Every invention ever made or thought of must have at some stage undergone a process of few or many stages before it was either implemented, scrapped or both.

It is through these various stages we as people have developed the world and everyday items around us, so it was only a matter of time (the late 60’s) before we refined and implemented these design structures to be used within the fledgling computer industry.

There are many different systems in use today, no one of them being better than the next but when choosing one you must be confident that it’s right for the project you are about to embark on.

Waterfall Model

The waterfall method of system design was developed during the late 1960’s. It was the first attempt at a methodical approach for system design. It is a completely methodical and comprehensive approach with different stages to follow throughout the process. The objectives of such a system are threefold, firstly to ensure that a high quality system is delivered, secondly to be able to maximize the productivity of the systems staff and lastly to provide strong management control over the system production. The main stages of development are:

Feasibility study

This is where we carry out and gain an understanding of the customers current system and document using DFD’s, entity modelling and normalisation.

Requirements analysis

This is where we break down what are our new system requirements are e.g. software and hardware needs.

Design

At this stage we would make an overall design of the system architecture and any faults should definatley be identified before moving onto the next stage. Build project dictionary.

Coding and testing

The programmers now begin programming the code and ...

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Feasibility study

This is where we carry out and gain an understanding of the customers current system and document using DFD’s, entity modelling and normalisation.

Requirements analysis

This is where we break down what are our new system requirements are e.g. software and hardware needs.

Design

At this stage we would make an overall design of the system architecture and any faults should definatley be identified before moving onto the next stage. Build project dictionary.

Coding and testing

The programmers now begin programming the code and beta testing it. We would also train the people who will be using the new system.

Conversion

This is also sometimes called integration, where we assemble all the pieces of the new system together and see if it matches up to the original system requirements.

Post implementation review

This is where the software would be delivered to the customer and is ready for acceptance testing. Operating documentation will be generated and the procedures for the system will also be documented.

The main benefits of using an SDLC such as the waterfall model (some people prefer to call it a method) are it provides a structured approach to design, from the initial need for a new system to be recognised to the detailed lyses of the business and practises of the business a systems analysis can take an in depth look at how things relate to each other, remove any duplicity with in current systems and the employer can (for many for the first time) see how their business or computer system works. It is therefore also an ideal time to restructure or reorganise a business or system. This system can also be incorporated and is known as PISO (process improvement for strategic objectives).

The main downfalls of the waterfall model are that the waterfall model assumes from the outset that you know exactly what kind of system you would like and by doing this it leaves no scope whatsoever for making late changes or implementing new ideas at a later stage. The standard methods for calculating cost of the system are calculated using COCOMO developed by Dr. Barry Boehm while he was at TRW [Boehm, B., 1981:] Software Engineering Economics, Prentice Hall]. Generally this states that by every stage the cost will multiply by a factor of 10, so the outcome of this is that the Waterfall model is an expensive method to use.

To not use an SDLC would be suicidal, as many people have found out to their own cost in the past, to simply implement ideas and software without using a solid, tried and tested method is I suppose like jumping into a car without an idea how to drive. To design and implement a new system you must use a life cycle model whether or not the Waterfall model must be determined, there are many others.

To compare the Waterfall model against two other models I have drawn up a table, on this table I’ll compare the Waterfall model to the Incremental and Prototype models.