The Defense Contract Management Agency (DCMA) 14-point assessment prefers the finish-to-start (FS) relationship for defining the interface between activities. Let’s take a look in more detail.
The DCMA 14-point assessment was developed to support inspecting the quality of schedules. Project schedules that conform to the DCMA 14-point assessment guidelines are higher quality schedules, and have a significantly greater opportunity for success.
Of particular importance in the 14-points assessment are the relationships between activities. Activity relationships make schedules more dynamic, so that the effects of schedule change propagate through the schedule. This means that activity start and finish dates automatically respond and update to changes in the schedule or to progression of the schedule.
The dynamic nature of a schedule is an important measure of its quality. But it is not enough for a schedule to be dynamic, it also must be understood by stakeholders. Much of the clarity of a schedule is determined by the types of relationships defined between activities. Transparent schedule relationships are therefore an important measure of a schedule’s quality.
This article discusses why the DCMA assessment prefers the insertion of FS relationships to define the interface between activities.
The FS relationship is the most common scheduling relationship. The precedence diagram for a FS relationship, Figure 1, says Task B cannot start until Task A finishes. The tasks in the FS relationship are sequential, activity B takes place after activity A.
In addition to the FS relationship schedulers also have start-to-start (SS), start-to-finish (SF), and finish-to-finish (FF) relationships in their arsenal of relationship tools. Precedence diagrams for these relationships are displayed in Figures 2, 3, and 4.
All four of these relationship types are acceptable according to the 14-point assessment. Note, however, that the SF relationship is considered to be somewhat counterintuitive, where successor activity B occurs earlier in time than predecessor activity A. Without delving into further detail about the SF relationship, and in the interest of schedule simplicity, it is best to limit the insertion of SF relationships in the schedule to extremely rare situations.
The 14-point assessment does not forbid SF relationships nor any of the other relationship type. It does, however, specify in the interest of schedule transparency that at least 90% of all activity relationships should be of the FS type. While not completely outlawed by the DCMA 14 assessment, there have been various of examples of its eradication written into some government contracts.
Though their usage should be limited, SS and FF relationships in particular, are acceptable in situations where they describe the true nature of the dependency. This is when activities performed in parallel either are restricted by predecessor, Task A, having to start first or by predecessor, Task A, having to finish first. For example you would not proceed with mobilization, Task B, until the project as begun, Task A, a standard SS relationship. It’s also logical that ongoing quality assurance inspections cannot not finish, Task B, until production of the product being inspected is complete, Task A, a classic FF relationship. If these activities, however, do not truly have the FS dependency; SS and FF relationships should not be used to simply fast track a schedule, (i.e. shorten a schedule by taking sequential activities and performing them in parallel) without legitimizing this by augmenting the resource pool needed to perform such parallel work.
As the FS relationship is sequential, where activity A must complete before progressing to activity B, it is easy to understand. And, as mentioned above, it is for this clarity that the 14-point assessment encourages the use of the FS relationship. Yes, SS and FF relationships composing ten percent or less of schedule relationships are acceptable.
Schedulers, however, should restrain from applying SS and FF relationships simply to model relationships in parallel. It is possible to implement FS relationships and model activities in parallel by assigning parallel FS dependent activities the same predecessor.
So be extremely cautious about the insertion of an SF relationship. And SS and FF relationships are appropriate where a true dependency is present. However, for schedule simplicity use of FS relationships is encouraged. Other relationship types are more difficult to trace and understand. As a general guideline, the 14-point assessment says 90% of schedule dependencies should be FS. This ensures a simpler and more logical flow through the schedule.
Note also that you can maintain FS dependencies and model activities in parallel by assigning parallel FS dependent activities the same predecessor.
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