Project Network Diagrams: Important Tool for Project Time Management

Management of a project brings about many challenges for the project manager. One of the frequently encountered challenges is in the arena of Time Management. As any practicing project manager can attest, time is one of the most important project constraints frequently encountered in practice. The other two project constraints are project budget and project scope. Time constraint can be particularly challenging when customer imposes a predetermined target completion date even before the project planning begins or is still in-progress. And to compound this further, the customer imposed target date is usually ahead of the planned completion date. So, what is a project manager supposed to do under such circumstances?

Project Time Crunch: Handling Options

Project managers must carefully consider all possible options that can assist in matching the planned project completion date to customer specified completion date when the latter date is earlier than the former date. As a starting point, project manager can determine if schedule compression techniques can help in meeting the target date, and if that doesn’t work then negotiate two possible alternatives with project sponsor(s) and key stakeholders:

Reduce number of objectives/deliverables for the project. This reduces scope which in turn assists in reducing work and thus can help to make the target date achievable, or

Negotiate to change the target completion date for the project to at least match the planned completion date.

Prior to escalating the matter to sponsor and/or key stakeholders, it is advisable to explore if schedule compression can help. Schedule compression involves two techniques-Crashing and Fast-tracking. Crashing involves assignment of additional resources to tasks in order to assist in completing them faster. Fast-tracking involves performing several tasks concurrently especially if they have no direct dependency on one another and can be done in parallel. Now, crashing does increase project cost due to the employment of additional resources and for this project manager must take into consideration the project budget along with contingency reserve to ensure project costs does not exceed available funds. Note that a project manager can employ both the techniques in the same project if necessary.

Project Network Diagrams

In order to decide on the schedule compression approach and which tasks should be brought under the purview of which schedule compression approach, project manager must use the project’s network diagram also known as Network Logic Diagram. Let’s now understand the role that Project Network Diagram (PND) or Network Logic Diagram (NLD) can play in assisting project managers undertake schedule compression. PND can be of two types: Activity-on-Arrow (AOA) and Activity-on-Node (AON). Activity-On-Node (AON) PNDs are also known as Precedence Diagramming Method (PDM). In this article, I will focus on AONs or PDMs as they are more popular and frequently used in practice and in software such as Microsoft Project.

PDM/AON & CPM: Understanding Benefits

AONs are created based on activities or tasks obtained from the project’s Work Breakdown Structure (WBS). While WBS provides several details such as which tasks when completed can provide which project deliverable, it does not incorporate relationships or dependencies between tasks. Dependencies between tasks are either graphically depicted or described in tabular format for a PND. This helps in understanding the type of relationship between tasks and in what sequence they should be performed. In addition, PNDs can have multiple task sequences and each such sequence from start of project to finish defines a specific path in the PND. The delineation and understanding of all paths in a PND are important as it lays the groundwork for determining planned duration of the project as well as those tasks which directly impact the project’s completion date and thus cannot be delayed. A very specific method called Critical Path Method (CPM) is used for PNDs like AONs in order to determine the following:

  • Planned project completion date
  • Early start and finish times for each task in the PND
  • Late start and finish times for each task in the PND
  • Available Slack or Delay time for each task and the project itself
  • One or more critical tasks and paths in the PND

Arming oneself with all the details above can greatly assist in determining the following:

  • Which tasks can be delayed and which tasks cannot be delayed
  • Analyze dependencies to determine which tasks can be done concurrently in order to undertake fast-tracking if necessary
  • What is the planned total duration of the project?

Closing Thoughts

It must not be difficult to understand now that PNDs such as AONs is an important tool in a project manager’s toolbox to use in order to handle time constraint challenges or simply undertake schedule planning for a project. Knowledge of this very important tool along with application of network analysis technique called Critical Path Method (CPM) is a required skill even when it is done using robust scheduling software like Microsoft Project. This is because the actual task dependency set up even in Microsoft Project must be done by the project manager and it is often necessary to go beyond the defaults used by the software. It is then and only then that the software’s true power of being able to generate what-if scenarios can be utilized to the max which obviously cannot be done by always relying on software defaults. In addition to task dependencies, tasks can be set to have lead or lag times as well. Lead time is when a successor task is allowed to have a head start and can begin prior to completion of the predecessor task, and Lag time allows for the successor task to be delayed from starting by a defined time after the predecessor task completes.

Besides being useful in practice, anyone who aspires to get certified as a PMI’s Project Management Professional (PMP) or Certified Associate in Project Management (CAPM) will have to know all the basics regarding PNDs and use of CPM in order to prepare well for the important Project Time Management knowledge area. In this brief article I have focused on extolling the benefits of PDMs/AONs as they can significantly aid in management of project schedule and its constraint related challenges. I would like to encourage all readers new to this topic to consult any project management book that covers the basics of this topic in a comprehensive manner, and start using them in their projects.

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