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Understanding the PERT and Critical Path Aspects of Microsoft Project

written by: chemuturi • edited by: Marlene Gundlach • updated: 2/28/2013

Here you'll find an explanation of the little known facets of Microsoft Project. You'll find they are vital for effectively using the program to generate an accurate schedule.

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    For Scheduling and Tracking--And More!

    Microsoft Project is by far the most commonly used software tool for scheduling and tracking project activities in software development organizations. Still, there are a few vital gaps in its effective usage. This article covers some of the most common of these little known facts, which are vital for effective usage of MS Project.

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    Backbone of Microsoft Project

    MS Project is based on two project management techniques:

    1. Program Evaluation and Review Technique (PERT): This originated in the US Department of Defense as way of handling uncertainty inherent in its research and development projects.
    2. Critical Path Method (CPM): This originated in the construction industry mainly to predict the project completion data accurately and to reduce it by the application of more resources.

    Both techniques are based on network diagrams. A network diagram is a pictorial representation of the project in which activities are recorded on arrows, and events (milestones which signify completion of one or more activities) are recorded on nodes. All of the activities are embedded between the Start Event and the End Event. Both are concerned with the duration of the activity and the project. Therefore, an MS Project file should contain all activities between the Start and End Activities of a project.

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    Activity Relationships

    These network diagrams have developed into Precedence Diagrams in which the activity is on the node, and arrows show the relationship between activities and the direction of the flow. They depict four types of relationships between the activities:

    1. Finish to Start – to be able to start the successor activity the predecessor activity must be finished
    2. Start to Start – the successor activity can be started shortly after starting the predecessor activity
    3. Start to Finish – successor activity must be started to finish the predecessor activity
    4. Finish to Finish – successor activity must be finished to finish the predecessor activity

    MS Project is based on these Precedence Networking diagrams and allows each of the four types of relationships.

    Many using MS Project do not realize how these Precedence Networking diagrams function. If no relationship is explicitly defined, it assumes a Finish-to-Start relationship. In reality, we use Start-to-Start relationships more frequently, or at least as frequently as the Finish-to-Start relationship. When we do not use the proper relationship, the resulting schedule cannot be realistic.

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    Dangling Nodes

    As MS Project is based on the Precedence Diagramming technique, it is essential that all activities must be embedded between a Start Activity and an End Activity. Every activity must be connected (through other activities or directly) to both the Start and End Activity. In other words, every activity must be on a path that begins at the Start activity and terminates at the End activity. When an activity is not connected to either a Start or End Activity, it is called a Dangling Activity. You can view these Dangling Activities in the Network Diagram View of MS Project. The presence of Dangling Activities causes a schedule to be erroneous. Therefore, all Dangling Activities must be placed on a path between Start and End Activities.

    If you want to use MS Project effectively, learn PERT/CPM to properly follow these activity patterns.

    There is also a great series on Microsoft Office Project 2007 you will want to read.