exxcel_logo.jpg (4387 bytes)

wpe1.jpg (2377 bytes)

3.6.2 Terms and Definitions

 

Up

 

.2 Key Terms and Definitions

Work Breakdown Structure

A Work Breakdown Structure (WBS) is a 'family tree' of the project tasks and deliverables required to deliver the final product. It is usually broken down into phases, activities, and tasks as illustrated below:

35c.gif (10179 bytes)

 

Elapsed Time vs. Duration vs. Effort

There is often considerable confusion when discussing the differences between elapsed time, duration, and effort. The following defines these terms and shows the equivalent relationship to the MS Project tool.

Elapsed Time

This is the elapsed calendar time (days, weeks, months, etc.), including holidays and other non-working days, required to complete a given activity. In MS Project, this is the number of days between the scheduled start and finish dates of a task.

The Construction Industry often refers to elapsed time as "Calendar Days".

Duration

This is the amount of time (hours, days, weeks, months, etc.), not including holidays and other non-working days, necessary to complete the work required for a given activity. MS Project utilizes a 'Duration' field that is consistent with this definition. The Construction Industry often refers to duration as "Work Days".

 

Effort (Work)

This is the number of work units required to complete a given task. Work units are usually expressed as hours, days, or weeks. "Effort" in MS Project is called "Work".

Effort and Duration are intricately tied together. For example:

A 5-day task (effort), where the resource is working at 100% availability on the task, will have a duration of 5 days.
A 5-day task (effort), where the resource is working at 50% availability on the task, will have a duration of 10 days.
This concept is covered in further detail in Step 5 of this technique.

NOTE: Resource availability in MS Project is defined by using the "Resource Max. Units'" field. If the Resource Max. Unit = 1, the resource is allocated at 100%. If the Resource Max. Unit = 0.5, the resource is allocated at 50%.

 

Gantt vs. PERT

The Gantt Chart and PERT Chart are two distinct tools for displaying schedule information. Each serves a specific purpose when building the project schedule. Both of these charts are readily available in MS Project.

Gantt Chart

This is a graphic display of schedule-related information. In the typical Gantt Chart, tasks are listed down the left side of the chart, dates are shown across the top, and activity elapsed times are shown as date-placed horizontal bars. The following are examples of a Gantt Chart:

wpe6.jpg (21899 bytes)

Click the "thumbnail" image below to view a full size image of the Gantt Chart.

36_gantt.bmp (2285632 bytes)

 

PERT Chart

The PERT Chart uses a network diagramming technique in which tasks are represented by boxes. Tasks are linked by logical relationships or dependencies to show the sequence in which the tasks are to be performed. The PERT Chart in MS Project also automatically calculates the Critical Path. The Critical Path is the sequence of tasks (or path) that will take the longest to complete. The Critical Path may change from time to time as tasks are completed ahead of or behind schedule. The following is an example of a PERT chart:

Click the "thumbnail" image below to view a full size image of the PERT Chart.

wpe8.jpg (99090 bytes)

 

Dependency

A dependency is a logical relationship between two project tasks, or between a project activity and a milestone. The four possible types of logical relationships are as follows:

Finish to start -The 'from' activity must finish before the 'to' activity can start.
Finish to finish - The 'from' activity must finish before the 'to' activity can finish.
Start to start - The 'from' activity must start before the 'to' activity can start.
Start to finish - The 'from' activity must start before the 'to' activity can finish.

Lag Time

This is a modification in the dependency where there is a delay in the start of the successor task. For example, in a finish-to-start dependency, with a 10-day lag, the successor activity cannot start until 10 days after the predecessor has finished.

Lead Time

This is a modification in the dependency where there is acceleration in the start of the successor task. For example, in a finish-to-start dependency, with a 10-day lead, the successor activity can start 10 days before the predecessor has finished.

Slack Time

This is the amount of time that an activity may be delayed from its early start without delaying the project finish date. Slack can change as the project progresses and changes are made to the project plan.

Milestone

A milestone is a significant event in the project, usually completion of a major deliverable. Milestones may also be used to produce summary level schedules (called 'Master Schedules') that depict major tasks and key milestones. In MS Project, milestones are typically represented as tasks with zero duration.

Back Home Up Next

 March 29, 2000
Copyright EXXCEL Contract Management Inc. 1998. All rights reserved.
Please feedback via email to jhoess@exxcel.com