Schedule Risk Analysis Simplified

摘要

The critical path method (CPM) of scheduling a project is a key tool for project management. A schedule "network" represents the project strategy. Activities, where the work is accomplished, are linked by relationships (e.g. finish-start, start-start, finish-to-finish) showing how the work is planned. Strings of linked predecessor and successor activities constitute "paths" through the network. When two or more paths are to be done simultaneously, they are described as parallel paths. Some of the most important points in the project are where several parallel paths converge. At these merge or join points, the paths must all be completed before a milestone is recorded for payment, an inspection can be done, sub-assemblies can be integrated for testing or the project can be recorded as complete. CPM computes the shortest project completion duration and or completion data from the longest path through the network. The "longest pole in the tent" is called the "critical path". Any delay on the critical path will delay the project. Conversely, CPM shows that paths that are not critical can be delayed or lengthened, if they have enough "float" or scheduling flexibility, without necessarily delaying the project. On the one hand, the critical path method (CPM) of scheduling is traditional and well-accepted. It is essential for developing the logic of the project work and for managing the day-to-day project activites. On the other hand, the CPM schedule is only accurate if every activity is started "as soon as possible" and takes just as long as its duration estimate indicates. Project managers understand that projects do not ever go entirely according to plan, which is one reason for frequent status reviews. Since real projects do not work this way, CPM is just the beginning of project schedule management.