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What is a Summary or Hammock Activity?

A summary or hammock activity, shown in ACTIVITY CHART , is used to represent groups of activities in a project schedule. It is used to summarize the schedule information for a group of activities and to allow the entire project to be summarized as a relatively few summary activities. The summary activity shows the start and finish for a group of activities as one Gantt bar. If the early starts and early finishes are being used for the schedule, the bar will show the earliest early start and the latest early finish for any of the activities in the group.

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The summary activity has come into use since the development of project management software. The advantage of summary activities over milestones is that it is not necessary to set up elaborate logical relationships to make sure that the milestone is rescheduled when activities in the group represented by the milestone are moved.

The milestone shows only a single date. This can be the start or finish of a group of activities, or it can be some major event or commitment date. The summary activity shows the start and finish for a group of activities. The computer will search through the group of activities and find the earliest early start date and the latest early finish date if the project is being scheduled according to the early schedule. If the project is being scheduled by the late schedule or a combination of the two, the computer will search for the earliest and the latest scheduled dates in the group of activities.

On the Gantt chart the milestones will have a duration of zero and are generally shown as triangles. Summary activities are shown on the Gantt chart as schedule activity bars and usually have a graphic to distinguish them from the normal scheduled activities. In Microsoft Project the summary bars have small triangles below the bar at each end of the bar. The summary activities are created by selecting the activities to be summarized and clicking on the right arrow on the tool bar above them.

The work breakdown structure is entered the same way. The WBS will make a convenient set of summary activities and may be sufficient for your reporting system. If not, other summary activities may be entered as needed.