In which of the following logical relationships can the successor activity not begin until the predecessor activity has completed?

This process is where the activities given in the activities list, the output of the previous process 6.2 Define Activities, are analyzed to see which of them should logically come before others.   There are three basic techniques, the precedence diagramming method (PDM), dependency determination and integration, and the adding of leads and lags between activities as needed.    The basic tool of this process is the Project Management Information System or PMIS (such as Microsoft Project).

6.3.2  Sequence Activities:  Tools and Techniques

6.3.2.1  Precedence Diagramming Method (PDM)

The precedence diagramming method represents activities by boxes called nodes.   If a certain activity logically comes before another activity that it is dependent upon, then that is called a predecessor activity.    And conversely, if a certain activity logically comes after another activity in a schedule, then that is called a successor activity.    It is the next technique, Dependency Determination and Integration, which can help determine which activities are connected logically in this manner.

This is the “precedence” part of the method.   The diagramming part comes next, where the activities are represented by rectangular boxes called nodes.   These nodes are then linked depending on the type of dependency or logical relationship between them.

There are four types of logical relationships between a predecessor and a successor activity.    Two are series relationships, where the activities are done one after the other.  Two are parallel relationships, where the activities partially overlap in time.

With the following four designations that consist of the two letters “F” (for “finish”) and “S” (for “start”), the first letter refers to the predecessor activity and the second letter refers to the successor activity.

• Finish-to-start (FS)–this is the most common type of logical relationship, where a successor activity cannot start until the predecessor activity has finished.
• Finish-to-finish (FF)–this is the next most common type of logical relationship, where a successor activity cannot finish until the predecessor activity has finished.  However, the activities can overlap in time.   The example used in the PMBOK® Guide is where you must finish writing a document (the predecessor activity) before you can finish editing it (the successor activity).   However, once you get a few pages of the document written, you can start editing those pages before you continue writing the rest of the document, so the writing and the editing of a document can occur overlap in time.
• Start-to-start (SS)–this is the next most common type of logical relationship, where a successor activity cannot start until the predecessor activity has started.   The example used in the PMBOK® Guide, the activity of leveling the concrete (the successor activity) cannot begin until pour foundation (successor activity) begins.  Although you can start leveling the concrete that has already been poured in one section of the foundation while another section of the foundation is being poured, you cannot level concrete before it has been poured.
• Start-to-finish (SF)–this is the least common type of logical relationship, where a successor activity cannot start until the predecessor activity has started.   This is very rarely used, although the example used in the PMBOK® Guide  is that a new accounts payable system (successor activity) has to successfully start up before the old accounts payable system is shut down (predecessor activity).

6.3.2.2  Dependency Determination and Integration

The dependencies between activities can be characterized by certain attributes, some of which are mutually exclusive.   Dependencies can be either a) mandatory or discretionary, and b) external or internal.

• Mandatory dependencies–dependencies that are legally or contractually required or inherent in the nature of the work.
• Discretionary dependencies–dependencies that are established through general best practices within a particular application area.

Discretionary dependencies are not “set in stone” as the mandatory dependencies are.   This is important because they can be modified if necessary, whereas mandatory dependencies cannot be so modified.

Here’s the other set of mutually exclusive attributes.

• External dependencies–dependencies that are usually outside of a project team’s control
• Internal dependencies–dependencies that are generally inside of a project team’s control

Those internal dependencies that are inside of a project team’s control are therefore more easily modified if necessary as compared to external dependencies.

6.3.2.3  Leads and Lags

A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity.    A two-week lead for a successor activity would mean that it could be started two weeks prior to the completion of the predecessor activity.

A lag is the amount of time a successor activity can be delayed with respect to a predecessor activity.   A two-week delay lag for a successor activity would mean that it could only be started two weeks after the completion of the predecessor activity.

If you would like to see an example exam question involving the precedence diagramming method, including leads and lags, you can go to the following post I did in reviewing the 5th Edition of the PMBOK® Guide.

https://4squareviews.com/2013/03/31/5th-edition-pmbok-guide-chapter-6-precedence-diagramming-method-leads-and-lags/

6.3.2.4  Project Management Information System (PMIS)

This is the scheduling software that you use to help sequence the activities (such as Microsoft Project or Primavera).

The next post will show the outputs of this process.

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