Page "Earned value management" Paragraph 26

The first step is to define the work.

This is typically done in a hierarchical arrangement called a work breakdown structure ( WBS ) although the simplest projects may use a simple list of tasks.

In either case, it is important that the WBS or list be comprehensive.

It is also important that the elements be mutually exclusive, so that work is easily categorized in one and only one element of work.

The most detailed elements of a WBS hierarchy ( or the items in a list ) are called activities ( or tasks ).