Define Activities is one of the 42 project management processes outlined in the fourth edition PMBOK®. It’s categorized as one of the six Time knowledge area processes, and one of the twenty Planning processes. The purpose of this process is to identify the specific tasks needed to be done in order to produce the project’s deliverables. The Scope Baseline is used as a starting point to breakdown the documented deliverables even further, as well as a guide to assure that the entire scope of the project is covered, but that the activities do not extend beyond the boundaries of the project. The Scope Baseline, an output of the Create Work Breakdown Structure (WBS) process, comprises three things—the WBS, WBS dictionary and the Project Scope Statement.
Decomposition is a tool and technique of Define Activities, just like the Create WBS process; here the work is being decomposed to a more detailed level than it was in the Create WBS process. Define Activities involves examining the lowest level of the WBS, called work packages, and breaking them down even further into activities. For example, if a work package was “bake a birthday cake,” the activities derived from this could include: select recipe, determine which ingredients needed to be bought, buy ingredients, preheat oven, mix ingredients, place ingredients in cake pan, place in oven, and remove from oven when done. The outputs of this process are the Activity List, Activity Attributes, and Milestone List. The Activity List is simply the list of activities, whereas Activity Attributes can document a number of things about each activity, for example, who is responsible, which activities must come first, constraints and assumptions. In summary, Define Activities creates a list of activities based on the deliverables defined in the WBS.