M G M T 4880 chapter 6

The Project Network

A flow chart that graphically depicts the sequence, inter dependencies, and start and finish times of the project job plan of activities that is the critical path through the network.

\ What is a hammock activity, and when is it used?

A hammock activity is a special purpose activity that exists over a segment of the life of the project. A hammock activity typically uses resources and is handled as an overhead cost—e.g., inspection. Hammock activities are used to identify overhead resources or costs tied directly to the project. The hammock duration is determined by the beginning of the first of a string of activities and the ending of the last activity in the string. Hammock activities are also used to aggregate sections of projects to avoid project detail—e.g., covering a whole subnetwork within a project. This approach gives top management an overview of the project by avoiding detail.

Laddering

Activities are broken into segments so the following activity can begin sooner and not delay the work.

Parallel (Concurrent) Activities

Activities that can occur independently and, if desired, not at the same time

Forward Pass Computation

Add activity times along each path in the network (ES + Duration = EF). Carry the early finish (EF) to the next activity where it becomes its early start (ES) unless... The next succeeding activity is a merge activity, in which case the largest EF of all preceding activities is selected.

Hammock Activity

An activity that spans over a segment of a project. Duration of hammock activities is determined after the network plan is drawn. Hammock activities are used to aggregate sections of the project to facilitate getting the right amount of detail for specific sections of a project.

What is the difference between free slack and total slack?

Free slack usually occurs at the end of an activity chain—before a merge activity. It is the amount of time the activity can be delayed without affecting the early start of the activity immediately following it. Since free slack can be delayed without delaying following activities, it gives some resource flexibility to the project manager. Total slack is the amount of time an activity can be delayed before it becomes critical. Use of total slack prevents its use on a following activity.

Free Slack (or Float)

Is the amount of time an activity can be delayed after the start of a longer parallel activity or activities. Is how long an activity can exceed its early finish date without affecting early start dates of any successor(s). Allows flexibility in scheduling scarce resources.

Practical Considerations

Network Logic Errors Activity Numbering Use of Computers to Develop Networks Calendar Dates Multiple Starts and Multiple Projects

Basic Rules to Follow in Developing Project Networks

Networks typically flow from left to right. An activity cannot begin until all preceding connected activities are complete. Arrows indicate precedence and flow and can cross over each other. Each activity must have a unique identify number that is greater than any of its predecessor activities. Looping is not allowed. Conditional statements are not allowed. Use common start and stop nodes.

Why is slack important to the project manager?

Slack is important to the project manager because it represents the degree of flexibility the project manager will have in rearranging work and resources. A project network with several near critical paths and hence, little slack, gives the project manager little flexibility in changing resources or rearranging work.

Backward Pass Computation

Subtract activity times along each path in the network (LF - Duration = LS). Carry the late start (LS) to the next activity where it becomes its late finish (LF) unless The next succeeding activity is a burst activity, in which case the smallest LF of all preceding activities is selected.

Why bother creating a WBS? Why not go straight to a project network and forget the WBS?

The WBS is designed to provide different information for decision making. For example, this database provides information for the following types of decisions: a. Link deliverables, organization units, and customer b. Provide for control c. Isolate problems to source d. Track schedule and cost variance. Network doesn't. e. Assign responsibility and budgets f. Focus attention on deliverables g. Provide information for different levels in the organization.

Sensitivity

The likelihood the original critical path(s) will change once the project is initiated. The critical path is the network path(s) that has (have) the least slack in common.

Lags

The minimum amount of time a dependent activity must be delayed to begin or end.

How are W B S and project networks linked?

The network uses the time estimates found in the work packages of the WBS to develop the network. Remember, the time estimates, budgets, and resources required for a work package in the WBS are set in time frames, but without dates. The dates are computed after the network is develped An activity that spans over a segment of a project. Duration of hammock activities is determined after the network plan is drawn. Hammock activities are used to aggregate sections of the project to facilitate getting the right amount of detail for specific sections of a project.

Why are lags used in developing project networks?

Two major reasons: a. To closer represent real situations found in projects b. To allow work to be accomplished in parallel when the finish-to-start relationship is too restrictive.

Event

a point in time when an activity is started or completed. It does not consume time.

Path

a sequence of connected, dependent activities.

How does the W B S differ from the project network?

a. The WBS is hierarchical while the project network is sequential. b. The network provides a project schedule by identifying sequential dependencies and timing of project activities. The network sets all project work, resource needs, and budgets into a sequential time frame; the WBS does not provide this information. c. The WBS is used to identify each project deliverable and the organization unit responsible for its accomplishment within budget and within a time duration. d. The WBS provides a framework for tracking costs to deliverables and organization units responsible.

Burst Activity

an activity that has more than one activity immediately following it (more than one dependency arrow flowing from it).

Merge Activity

an activity that has two or more preceding activities on which it depends.

Activity

an element of the project that requires time.

Critical path

the longest path through the activity network that allows for the completion of all project-related activities; the shortest expected time in which the entire project can be completed. Delays on the critical path will delay completion of the entire project.

Activity-on-Node (A O N)

uses a node to depict an activity

Activity-on Arrow (A O A)

uses an arrow to depict an activity