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Project Time Management – Part 2 Activity Sequencing
By Raymond Keckler | February 6, 2008
In the previous post on Project Time Management, I talked about the first process, activity definition. Activity definition identifies the deliverables at the lowest level in the work breakdown structure. After you have this list, what do you do with it? You put them in order. Activity sequencing involves identifying and documenting the logical relationships among scheduled activities (PMBOK 130). The deliverables are put in a logical order of precedence. The outputs of the activity definition provide the inputs for the activity sequence process.
- Project Scope Statement
- Activity list
- Activity attributes
- Milestone list
- Approved change request
Activity sequencing uses several tools and techniques to complete its task. The activity list must be organized into a logical order. Precedence must be determined to ensure some activities are done before or after other activities. By setting up a proper sequence, we can create a realistic and feasible project schedule.
Precedence diagramming method (PDM) is one of the tools used in activity sequencing. PDM constructs a project schedule network diagram that uses boxes to represent activities and connects them with arrows to show dependency (PMBOK 132). These boxes are called nodes so the precedence diagramming method is also called activity on node (AON). This is the most common method. The PDN uses four types of precedence.
- Finish to start – the activity can not begin until the previous activity is complete.
- Finish to finish – the activity can not finish until the previous activity is finished.
- Start to start – the activity can not start until the previous activity has started.
- Start to finish – the activity can not finish until the previous activity has started.
The finish to start is the most common type of precedence, and the start to finish is hardly ever used.
The arrow diagramming method (ADM) is another tool. The ADM uses arrows to represent activities and connects them with boxes or nodes to show their dependency. This is the opposite of the precedence diagramming method. The arrow diagramming method is also known as the activity on arrow (AOA). The ADM only uses the finish to start type of precedence. The ADM can also use dummy relationships to show logical relationships. The dummy relationship is shown as a dotted line on the ADM. Since the dummy relationship is not an actual activity, the duration is zero. The duration is the time it takes to complete an activity. The dummy relationship has no “work” so no duration.
Schedule network templates are just that - templates. They are standardized project schedule network diagram templates that are used to expedite the preparation of activities. They can be used to show such items as floors in a building or the startup phase for a development project. When the activities are going to be the same, use a template.
One activity might be dependent on another activity. You will use the different types of precedence to describe the dependencies. In the dependencies, there might be a need to have a lead or a lag between activities. An activity might be pouring cement; however you must wait two days after it is poured before you can remove the cast around the cement. This two day wait is a lag. A lead allows the next activity to start before the previous one is finished. A lag directs the next activity to wait even if the previous activity is done.
When you are finished with activity sequencing you should have a project schedule network diagram, an updated activity list, an updated activity attributes list, and the requested changes that were revealed when setting up the diagram.
Part 1 of Series “Project Time Management”
A Guide to the Project Management Body of Knowledge, Third Edition, PMBOK Guide. Project Management Institute, Inc. Pennsylvania, 2004.
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