Sequence Activities Tools & Techniques

How To Sequence Project Activities
Steps to Sequence Project Activities

Sequence activities is the process of identifying activities essential for project success and establishing logical relationship among these activities. While developing the project schedule it is imperative that all project activities that relate to project success are identified. These identified activities are analysed for relationships that exists among them. This helps to construct a well structured and a logically correct project schedule network diagram. A logically correct schedule network can help the project team to concentrate on sequence of critical project activities.

This post intends to look into various tools and techniques that are available to sequence various project activities. Precedence Diagramming Method (PDM) is a method to construct schedule network diagram. PDM indicates schedule activities on nodes. These activities are graphically linked to each other using logical relationships. These relationships indicates the sequence in which the activities will be performed. Activity-on-Node (AON) is a schedule diagramming technique that uses PDM methodology.

Tools to Sequence Activities:

Four types of dependencies are used in establishing logical relationships. However, before knowing what these dependencies are it is important to understand what are predecessor and successor activities.

Predecessor Activity:

It is an activity that comes before a dependent activity in a project schedule.

Successor Activity:

It is an activity that comes after a dependent activity in a project schedule.

Predecessor_Successor_Activity
Predecessor & Successor Activity

In the figure above, activity P is predecessor activity of A and activity S is successor activity of A. However, activity A is also the successor activity of P and predecessor activity for S

The four dependencies used to sequence activities are:

Finish-to-Start (FS)

It is a logical relationship in which a successor activity (Activity B) cannot start until a predecessor activity (Activity A) has finished. It is the most commonly used dependency in scheduling software to establish logical relationship.

Finish-to-Start
Finish-to-Start

Start-to-Start (SS)

It is a logical relationship in which a successor activity (Activity B) cannot start until a predecessor activity (Activity A) has started.

Start-to-Start
Start-to-Start

Start-to-Finish (SF)

It is a logical relationship in which a successor activity (Activity B) cannot finish until a predecessor activity (Activity A) has started.

Start-to-Finish
Start to Finish

Finish-to-Finish (FF)

It is a logical relationship in which a successor activity (Activity B) cannot finish until a predecessor activity (Activity A) has finished.

Finish-to-Finish
Finish-to-Finish

Dependency Determination:

Project activities may also have following four attributes which helps to sequence activities.

  1. Mandatory Dependencies
  2. Discretionary Dependencies
  3. External Dependencies
  4. Internal Dependencies

Any two dependencies may be present at the same time in the following manner

  • Mandatory External Dependencies
  • Mandatory Internal Dependencies
  • Discretionary Internal Dependencies
  • Discretionary External Dependencies

Mandatory Dependencies

  • Also known as Hard Logic or Hard dependencies.
  • Legally or contractually required or inherit in the nature of work and involve physical limitations.
  • Technical dependency may not be mandatory and are not schedule constraints.
  • Project team determines which dependencies are mandatory.

Discretionary Dependencies

  • Also known as preferred logic, preferential logic, or soft logic.
  • Established based on best practices of an application area or when a specific sequence is desired.
  • Improper use may result in arbitrary total float.
  • During fast tracking these should be reviewed for modification or considered for removal.
  • Project team determines which dependencies are discretionary.

External Dependencies

  • Involve relationship between project activities and non-project activities.
  • These dependencies are usually outside the project team’s control.
  • The project management team determines which dependencies are external.

Internal Dependencies

  • Involve precedence relationship between project activities and are generally inside project team’s control.
  • The project management team determines which dependencies are external.

Leads & Lags:

Adding Lead and Lags to project schedule is another method to sequence activities.

Lead:

Lead is amount of time the successor activity (B) can be advanced with respect to predecessor activity (A). It is represented as a negative value of lag. For example FS-10 days.

Lag:

Lag is amount of time a successor activity (B) will be delayed with respect to predecessor activity (A). For example it is represented as SS+10 days.

 

Leads_Lags
Leads and Lags

Conclusion

Establishing logical relationship among various project activity is an important step in the schedule development process. Wrong relationships result in improper identification of critical path and puts the schedule control and resource allocation at risk.

To understand the schedule network analysis process, also read my post

To understand how to analyse a project schedule using critical path method you may also read

For steps involved in critical path analysis you may read the following

For complete list of PMP formulas please visit the resources page

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