PM Quiz 2 Chapter 6

Backward Pass—Latest Times

- How late can the activity start? (late start—LS) - How late can the activity finish? (late finish—LF) - Which activities represent the critical path? - How long can the activity be delayed? (slack or float— SL) •Subtract activity times along each path starting with the project end activity (LF - Duration = LS). •Carry the late start (LS) to the next preceding activity where it becomes its late finish (LF) unless... •The next succeeding activity is a burst activity, in which case the smallest late start (LS) number of all its immediate successor activities is selected.

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

1. A hammock activity is a special purpose activity that exists over a segment of the life of 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. 2.Hammock activities are used to: •Identify overhead resources or costs tied directly to the project, e.g., inspection. •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.

Total and Free Slack

1. Forward and backward passes must be finished before slack is calculated. 2. Both types of slack help us decide which activities can be delayed if necessary. 3. Total slack is shared across the whole path. If TS for one activity is used, ES for successors will be delayed and their TS reduced.

Critical Path is...

1. Is or are the network path(s) with zero total slack or the least slack in common. 2. Longest path through the activity network. 3. Shortest expected project completion time. 4. Important as it impacts completion time. 5. Where you put best people on. 6. Where you pay extra when doing risk assessment. 7. Is where you look when other managers asking to 'borrow' people or equipment. 8. Is where you look when you don't have time to monitor all activities.

Constructing a Project Network - Basic Rules

1. Networks typically flow from left to right. 2. An activity cannot begin until all preceding connected activities are complete. 3. Arrows indicate precedence and flow and can cross over each other. 4. Each activity must have a unique identify number. 5. An activity identification number must be greater than that of any predecessor activities. 6. Looping is not allowed. 7. Conditional statements are not allowed. 8. Use common start and stop nodes to indicate project beginning and end.

The Project Network

A flow chart that graphically depicts the logical sequences, interdependencies, and start and finish times of the project activities along with the longest path(s) through the network—the critical path.

Laddering

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

Total Slack for an Activity

Amount of time an activity can be delayed past EF and not delay the project. •SL = LS - ES = LF - EF •Affects whole project. •If negative => insufficient times for task and project will be delayed

Free Slack for an Activity

How long an activity can exceed its EF without affecting ES of successor(s). •Affects successor activities. •Can never be negative. •Allows resource scheduling flexibility. •FS only possible for activities at end of an activity chain with a merge activity.

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 than the project network, for decision making, such as: a. Link deliverables, organization units, and customer b. Provide for control c. Isolate problems to source d. Track schedule and cost variance. Network does not. e. Assign responsibility and budgets f. Focus attention on deliverables g. Provide information for different levels in the organization.

Critical Path

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

Lags

The minimum time a dependent activity must be delayed to begin or end. •Lengthy activities are broken down to reduce the delay in the start of successor activities. •Lags can be used to constrain finish-to-start, start-to-start, finish-to-finish, start-to-finish, or combination relationships.

What is the difference between total slack and free slack?

Total Slack for an Activity •Amount of time an activity can be delayed past EF and not delay the project. •SL = LS - ES = LF - EF •Affects whole project. •If negative => insufficient times for task and project will be delayed. Free Slack for an Activity •How long an activity can exceed its EF without affecting ES of successor(s). •Affects successor activities. •Can never be negative.•Allows resource scheduling flexibility. •FS only possible for activities at end of a chain with a merge activity.

Sensitivity

likelihood the original critical path will change ones the project was initiated.

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.

Path

a sequence of connected, dependent activities.

How does the WBS differ from the project network?

a. The WBS is hierarchical while the project network is sequential. b. The WBS is used to identify each project deliverable and the organization unit responsible for its accomplishment within budget and within a time duration. c. The WBS provides a framework for tracking costs to deliverables and organization units responsible. d. 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.

How are WBS and project networks linked?

a. Time estimates found in the work packages of the WBS are used to develop the network. b. 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 developed.

Activity

an element of the project that requires time (activity time or waiting time) but may or may not require resources.

Parallel Activities

can run simultaneously (but don't have to) depending on Project Manager's choice.

Level of Detail for Activities

•A Work Package consists of Tasks. •An Activity represents one or more tasks from a work package. •How many tasks you include in each activity sets the level of detail.

Using Forward and Backward Pass Info

•Free slack gives the Project Manager flexibility in scheduling scarce resources (people and equipment) that are used on more than one parallel activity or another project. •Knowing the four activity times (ES, LS, EF and LF) is invaluable for the planning, scheduling and controlling phases of the project. •When the critical path is known, resources can be tightly managed to avoid errors. Also, if the project must be shortened for any reason, the critical path will help us select the activities that will cost the least to shorten the project.

Forward Pass—Earliest Times

•How soon can the activity start? (early start—ES) •How soon can the activity finish? (early finish—EF) •How soon can the project finish? (expected time—TE) •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 early finish (EF) number of all its immediate predecessor activities is selected.

Practical Considerations

•Network Logic Errors •Activity Numbering •Use of Computers to Develop Networks (and Gantt Chart) •Calendar Dates •Multiple Starts and Multiple Projects

Three basic relationships between activities:

•Predecessor activities •Successor activities •Concurrent or parallel activities

Advantages of Project Network

•Provides the basis for scheduling labor and equipment. •Enhances communication among project participants. •Provides an estimate of the project's duration. •Provides a basis for budgeting cash flow. •Identifies activities that are critical. •Highlights activities that are "critical" and should not be delayed. •Help managers get and stay on plan.

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.

Hammock Activity

•Spans over a segment of a project. •Has a duration that is determined after the network plan is drawn. •Is very useful in assigning and controlling indirect project costs. •Is used to aggregate sections of the project to facilitate getting the right level of detail for specific sections of a project.

From WBS/Work Package to Network

•Work package is defined independently of other WPs, requires specific resources, has specific start + finish points, tech specifications, cost estimates. •Activity network includes dependency, sequencing, timing of work packages.