Life Cycles Birth to death! i.e what happens to a piece of software from the first appearance of the need for it to the time when it is finally retired from use. An attempt to address S/W problems by understanding the processes involved in each part of the software lifecycle. –classic text - “The mythical man-month” by Brooks, Addison Wesley Still the subject of research –Software Engineering journals the best source of modern information Shows the need for active management of the process Different lifecycle models have been used to help study software lifecycles –Waterfall model –Prototyping –Boehm’s spiral –Formal models

The Waterfall model Requirements definition System & software design Implementation & unit testing Integration & system testing Operation & maintenance

Difficulties with the waterfall model Real projects are rarely so sequential – there is always some iteration or backtracking, which is not ‘part of the plan’ and so causes management problems. It assumes the customers knows all the requirements exactly at the very start. This will often not be the case, particularly in a fast moving world where different techniques (especially in the area of user interfaces) are evolving all the time. It doesn’t produce anything visible for the customer until almost the end of the cycle, by which time, especially if there are any delays, the customer, or more likely the financial backer may be pulling their hair (and maybe their money) out! This, despite the fact that the project may be very healthy indeed.

Prototyping Mainly to validate user requirements, which may be unclear Throw away? or transform to final design Advantages –Can clear up misunderstandings (use of language) user/developer –Can identify missing user services –Developer can identify inconsistencies in requirements –Can provide a working model for managers/sponsors/accountants Disadvantages –Hard to manage –Temptation to use as real system –Features may be omitted –Not a good basis for any contract Outline specspecify system Develop prototype Evaluate prototype design & implement validate components