Identifying Missing Logic, Open Start, and Open Finish Activities by Using P6 Filters

“Critical Path Method” (CPM) scheduling is logic-driven and schedule dates are normally determined by implementing logical relationships between activities from the start to the finish of the project.

Identifying missing logic, open start and open finish activities should be part of logic assessment when it comes to schedule health check and will help to ensure:

a)      critical path reported by the scheduling software is realistic;

b)     the schedule can depict realistic consequences if the plan goes sideways.  

Many schedulers are quite familiar with the “missing logic” concept, and missing logic is usually checked in schedule assessments. however, not many schedules are being checked for open start and open finish activities.

Missing logic

Checking “Missing logic” is straightforward and activities that are missing predecessors or successors or both (AKA open-ended activities) are identified by performing this check. Ideally, no open-ended activities should be found in a schedule. Obviously the two exceptions are the first activity (e.g., project start milestone) and the last activity in the schedule (e.g., project finish milestone).

To identify open-ended activities in P6, you can create a filter similar to what is depicted in Fig 1.

Fig.1. A filter created in P6 for identifying open-ended activities

Open Start Activities

Generally speaking, the start date of each task in a schedule (excluding the project start milestone) should be driven or influenced by at least a predecessor (which can be a task or milestone). If there is at least one finish-to-start (FS) or start-to-start (SS) relationships between a successor and its predecessor(s), it means the start date of the successor can be influenced by at least one predecessor. If the relationships between the successor and its predecessors are just finish-to-finish (FF) or start-to-finish (SF), nothing will be driving the start date of the successor. In this case the successor is called an open start (aka a “Dangling Activity”). This rule does not apply to finish milestones. Finish milestones can have just finish-to-finish predecessors without being flagged as open start.

In version 16.1, Primavera introduced two useful fields called “Predecessor Details” and “Successor Details” and these two fields are the backbones of the filters created here for identifying open start and open finish activities (if you are using earlier releases of P6 you cannot use these filters)

In Fig.2, you can see the filter I created in P6 to identify open start activities. You might want to tweak it to fit your purpose.

               Fig.2. A filter created in P6 for identifying open start activities

?Open Finish Activities

An open finish activity (aka a “Dangling Activity”) is an activity that a significant delay in its finish date won’t drive/influence any successor (obviously the last activity in the schedule is not considered as an open finish activity). Any activity that has only start-to-start (SS) or start-to-finish (SF) successors is an open finish activity. This rule does not apply to start milestones. start milestones can have just start-to- start predecessors without being flagged as open finish.

In Fig.3, you can see the filter I created in P6 to identify open finish activities. (You might want to tweak it to fit your purpose).

Fig.3. A filter created in P6 for identifying open finish activities

Once identified, open ended, open start and open finish activities should be reviewed carefully, and realistic predecessors and/or successors should be linked to these identified activities.