network modelling

Techniques that enable complex projects to be scheduled, taking into account the precedence of each activity. Critical-path analysis (CPA) involves identifying all the activities that constitute the project to be modelled, determining their sequence or order of precedence, and estimating the time required for each activity. This information is used to build a graphical representation of the whole project and to establish the chain of activities that defines its overall length, i. e. the critical path. As well as being a powerful analytical tool, the visual qualities of CPA charts make them extremely useful aids to communications. With computer-based CPA programmes, managers can produce rapid updates when unexpected changes occur (e. g. the failure to complete an activity on time). These programmes also enable the appropriate resources to be allocated to the activities and detailed costings to be produced. The key to their successful use is that they should be updated continuously. Considerable resources are required to produce a CPA; if changes, postponements, etc. , are not noted the chart quickly becomes irrelevant. Programme evaluation and review technique (PERT) was developed in 1958 by the US Navy to assist in the construction of the first Polaris submarines. It is based on the same principles as CPA but uses statistical techniques to project optimistic, most probable, and pessimistic times for each activity.