5th Edition PMBOK® Guide—Chapter 6: Dependency Determination

1. Introduction

The last post discussed the time management process 6.3 Sequence Activities. The three tools & techniques of that process are listed below.

1. Precedence diagramming method (PDM) Used to construct a schedule model in which activities are represented by nodes and are linked to show the sequence in which they are performed.
2. Dependency determination Dependencies between activities are characterized by various attributes: mandatory vs. discretionary, internal vs. external
3. Leads and lags A lead is the amount of time a successor activity can be advanced with respect to a predecessor activity. A lag is the amount of time a successor activity can be delayed with respect to a predecessor activity.

The first one is a tool, the second and third are techniques. Must one activity done before another? If so, must it be complete before another one can be started? To answer questions like these, the second technique of dependency determination is used. This determines the nature of the dependency between any two activities, and is the subject of this post.

2. Types of Dependencies

Category Dependency Explanation
Mandatory vs. Discretionary Mandatory

(hard logic)


  • physical limitations
  • contractual or legal obligations

(soft logic)


Based on knowledge of best practices
External vs.


External Outside of project team’s control, based on relationship of project activities and activities outside project
Internal Within project team’s control, based on relationship between project activities

The reason for the classification into types of dependencies is that the mandatory and external types of dependencies cannot be changed or changed easily. The discretionary and internal types of dependencies can be changed more readily and therefore those activities that have these types of dependencies will be the ones the project manager should go to first if there is a necessity for crashing or fast-tracking in order to compress the schedule.

The next post will discuss the leads and lags technique, which is the third technique of those used in the process 6.3 Sequence Activities.


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