
Activity Sequencing and Project Logic
Determining the schedule of a project begins by examining each activity in the WBS to determine its relationship to the other activities.
Project Logic
The project logic is the development of the activity sequence or determining the order in which the activities will be completed. The process for developing the project logic involves identifying the predecessors - activities that come before - and successors - the activities that come after.
Project Logic for John's Move
In our example of
John's move, contacting Dion and Carlita – activity 1.1 – comes before the
lunch meeting is scheduled. You must logically contact Dion and Carlita
before you schedule your Host Planning Lunch – activity 1.2. Your
conversation with Dion and Carlita will provide you with dates they are
available and establish their commitment to help you move. Therefore,
the conversation with Dion and Carlita is a predecessor to the Host
Planning Lunch Activity. This relationship is diagramed below.
Figure 8.7 Relationship between Two Activities
These
terms define a relationship that is similar to a family relationship
like father and son. The father exists in time before the son.
Similarly, each element of the diagram can have predecessor-successor
relationships with other elements, just like a father can be the son of
someone else. Unlike the biological father-son relationship, activities
can have more than one predecessor.
The relationship between a predecessor activity and a successor activity is called a dependency. The successor activity starts after and is dependent on the predecessor activity. Because the conversation with Dion and Carlita must take place before a planning meeting can be scheduled, this is called a natural dependency because the relationship can be inferred logically. Activities that have predecessor-successor relationships occur sequentially - one after the other. Another term for this type of relationship is finish-start, which means the first activity must finish before the next one can start. Refer to the figure above.
Some activities take place concurrently - at the same time. If they must begin at the same time, they have a start-start relationship. If the activities can start at different times but they must finish at the same time, they have a finish-finish relationship. Refer to Figure 8.8.
Figure 8.8 Concurrent activities can be constrained to finish at the same time or start at the same time.