Page 145 - Project+

answer several other questions: How does the dependency impact the start and finish

of each of the activities? Does one activity have to start first? Can you start the second
activity before the first activity is finished? All these variables impact what your overall
project schedule looks like.

Once you identify a dependency between two activities, you need to determine what
that logical relationship is so that you can sequence the activities properly. Before
covering those relationships, I’ll present a few key terms related to understanding task
dependencies.

A predecessor activity is one that comes before another activity. A successor activity is
one that comes after the activity in question. Figure 5.1 shows a simple
predecessor/successor relationship between Activity A and Activity B.

FIGURE 5.1 A predecessor/successor relationship

Four possible logical relationships can exist between the predecessor activity and the
successor activity. Understanding these relationships will help you determine if you

can schedule the activities in parallel, or if one activity must wait until the predecessor
task is completed. The four logical relationships are as follows:

Finish-to-start (FS) In a finish-to-start relationship, the successor activity cannot
begin until the predecessor activity has completed. This is the most frequently used
logical relationship and is the default setting for most project-scheduling software
packages.

Start-to-finish (SF) In a start-to-finish relationship, the predecessor activity must
start before the successor activity can finish. This relationship is seldom used.

Finish-to-finish (FF) A finish-to-finish relationship is where the predecessor
activity must finish before the successor activity finishes.

Start-to-start (SS) In a start-to-start relationship, the predecessor activity must start
before the successor activity can start.

Once the activity dependency relationships have been identified, your next step is
creating a network diagram.

Creating a Network Diagram

One technique used by project managers to sequence activities is a network diagram.
Understanding activity relationships is fundamental to using this technique. A
network diagram depicts the project activities and the interrelationships among these
activities. A network diagram is a great tool to develop with the project team. Use a

145