Network Diagrams and Activity Sequencing

The purpose of activity sequencing is to identify and classify all time correlations among tasks by reviewing all activities in the WBS. These connections (i.e. “linkages”, “dependencies”, “predecessors”). Task timing connections are significant because they influence task sequencing as well as task start and finish dates. Task relationships are classified into four types:

A finish-to-start relationship: exists if one action must be completed before another begins

A start-to-start relationship: occurs if one action cannot begin until another begins

A finish-to-finish relationship: occurs if one action cannot be completed until another is completed

A start-to-finish relationship: arises when one action must begin before another can be completed.

The idea of a lag or a lead is associated with the assignment of task connections. Efficient project scheduling may make use of lag and lead periods, as well as task relationships, which change work length and start and finish dates. A lag time compels a task to begin at a time after that determined by established task linkages.

A project schedule will represent realistic timing considerations and allow for adequate overlap in the scheduling of activities to make the most use of time by effectively applying task relationships and lag and lead durations.

Once all dependencies have been established, a network diagram may be produced to represent the project sequencing visually. Arrows in network diagrams indicate tasks and are used to highlight dependencies.

The full network diagram may be used to identify a project’s critical path, which is the set of dependent activities that defines the project’s shortest possible length, providing all other milestones are completed on all other pathways. Trace all pathways indicated by arrows along the network diagram while adding the length of all tasks to discover the critical path. The critical path is the greatest total from start to finish. The critical path is properly named, as work on the critical path will cause a project to fall behind schedule if they take longer to complete than planned. Other tasks that are not on the critical path have variable degrees of slack, or the length of time a work may be postponed without jeopardising the completion deadline.