Scheduling consultants often mention “Missing Logic” as an obvious schedule quality check.
I believe it is not as obvious as it seems. This check may create an illusion of good quality of dependency data and hide critical issue(s) that may cause project delay.
The rule of thumb is “Each activity, except first and last activities, must have a predecessor and successor”. It is logical to have a metric that verifies if this rule is followed. This metric is known as the “Missing Logic” or “Open ends” metric. If a schedule has open-end activities, it requires attention.
However, if there are no activities without a predecessor and a successor, it DOES NOT mean there are no “lost” or “broken” dependencies in the schedule.
Even more, the “lost” dependency may impact the critical path and reduce the duration of the schedule, but the “open ends” metric still would be “Green”. It creates an illusion that the schedule doesn’t have issues with dependencies and no additional check is required. The “lost” and “broken” dependencies would not be identified until it is too late, and the project delivery dates are impacted.
A“broken” dependency is a dependency with incorrect characteristics (type, lag, ect).
Path Convergence & Path Divergence
Any schedule is likely to have activities with multiple predecessors and/or successors. It is possible that after a critical dependency has been removed, the schedule still doesn’t have open ends activities.
A relationship in which a scheduled activity has more than one predecessor.
A relationship in which a scheduled activity has more than one successor.
Critical Path: A B D E G
“Missing Logic” check: Green
Then a scheduler by mistake deleted one critical Dependency between D and E activities. Now the schedule has a new critical path and shorter duration, but the “Missing Logic” metric is still “Green” as all activities (except first and last) still don’t have open ends.
This example shows that we need another approach to manage the quality of dependencies.
The only way to check the quality of dependencies is to compare the list of dependencies against Corporate Norms or any other reliable set of dependencies, for example, in a baseline schedule.
As Primavera and MS Project users don’t have direct access to a list of dependencies, one of the options could be to load the schedule into the tool that has this capability.
Spider Project provides access to a list of all dependencies with all dependency characteristics: predecessor and successor codes and title, dependency type, lag, lag units, lag type, lag calendar, etc. Dependency quality analysis could be performed within the tool, or dependencies could be exported to Excel or BI tools.
“Missing Logic” metric is a required but not sufficient metric. It may create an illusion that the schedule dependencies are in good shape.
Dependency quality analysis have to be performed against reliable dependency data and incorporate analysis of both “lost” and “broken” dependencies.