Transcript Document 7298665
Project Management Project Time Management (Scheduling) Minder Chen, Ph.D.
CSU Channel Islands [email protected]
Time
• • •
Limited time is the one constraint of any project with which we are all probably most familiar. For many projects that create a product or event, time is the most important constraint to manage.
Project team members might not know the project budget or the scope of work in great detail, but chances are they all know the project deadline.
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Sample Time Constraints
• • •
You are building a house and must finish the roof before the rainy season arrives.
You are assembling a large display booth for a trade show that starts in two months.
You are developing a new inventory-tracking system that must be tested and running by the start of the next fiscal year.
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• • • • • • •
Project Time Management
6.1 Plan Schedule Management
—The process of establishing the policies, procedures, and documentation for planning, developing, managing, executing, and controlling the project schedule.
6.2 Define Activities
—The process of identifying and documenting the specific actions to be performed to produce the project deliverables.
6.3 Sequence Activities
—The process of identifying and documenting relationships among the project activities.
6.4 Estimate Activity Resources
perform each activity.
—The process of estimating the type and quantities of material, human resources, equipment, or supplies required to
6.5 Estimate Activity Durations
resources.
—The process of estimating the number of work periods needed to complete individual activities with estimated
6.6 Develop Schedule
project schedule model.
—The process of analyzing activity sequences, durations, resource requirements, and schedule constraints to create the
6.7 Control Schedule
—The process of monitoring the status of project activities to update project progress and manage changes to the schedule baseline to achieve the plan.
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Scheduling Overview
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Examples of Project Schedules
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• •
Project Schedule — Graphic Examples
Milestone charts.
These charts are similar to bar charts, but only identify the scheduled start or completion of major deliverables and key external interfaces.
Bar charts.
These charts, also known as Gantt charts, represent schedule information where activities are listed on the vertical axis, dates are shown on the horizontal axis, and activity durations are shown as horizontal bars placed according to start and finish dates.
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Project Schedule —Graphic Examples
Project schedule network diagrams.
These diagrams are commonly presented in the activity-on-node diagram format showing activities and relationships without a time scale, sometimes referred to as a pure logic diagram or presented in
a time scaled schedule network diagram
chart.
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Rules of performance measurement
Earned value management (EVM) rules or other physical measurement rules of performance measurement are set. For example, the schedule management plan may specify: • Rules for establishing percent complete, • Control accounts at which management of progress and schedule will be measured, • Earned value measurement techniques (e.g., baselines, fixed-formula, percent complete, etc.) to be employed • Schedule performance measurements such as schedule variance (SV) and schedule performance index (SPI) used to assess the magnitude of variation to the original schedule baseline.
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Rolling Wave Planning
• Rolling wave planning is an
iterative planning technique
in which the work to be accomplished in the near term is planned in detail, while the work in the future is planned at a higher level. It is a form of
progressive elaboration
.
• Therefore, work can exist at various levels of detail depending on where it is in the project life cycle. • During early strategic planning, when information is less defined, work packages may be decomposed to the known level of detail. As more is known about the upcoming events in the near term, work packages can be decomposed into activities.
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Milestone
•
A milestone is a significant point or event in a project
. A milestone list is a list identifying all project milestones and indicates whether the milestone is mandatory, such as those required by contract, or optional, such as those based upon historical information. • Milestones are similar to regular schedule activities, with the same structure and attributes, but they have
zero duration
because milestones represent a moment in time.
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Sequence Activities
Activity A is the predecessor of Activity B.
Activity B is the successor of Activity A.
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Precedence Diagramming Method
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• • • •
Dependency
Finish-to-start (FS).
has finished.
A logical relationship in which a successor activity cannot start until a predecessor activity has finished. Example: The awards ceremony (successor) cannot start until the race (predecessor)
Finish-to-finish (FF).
A logical relationship in which a successor activity cannot finish until a predecessor activity has finished. Example: Writing a document (predecessor) is required to finish before editing the document (successor) can finish. Editing task can start before Writing is finished.
Start-to-start (SS).
begins.
A logical relationship in which a successor activity cannot start until a predecessor activity has started. Example: Level concrete (successor) cannot begin until pour foundation (predecessor)
Start-to-finish (SF).
A logical relationship in which a successor activity cannot finish until a predecessor activity has started. Example: The first security guard shift (successor) cannot finish until the second security guard shift (predecessor) starts.
In PDM, finish-to-start is the most commonly used type of precedence
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relationship. The start-to-finish relationship is very rarely used.
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Dependency Determination
• • • •
Mandatory dependencies.
Mandatory dependencies are those that are legally or contractually required or inherent in the nature of the work.
Discretionary dependencies.
sequences. Discretionary dependencies are sometimes referred to as preferred logic, preferential logic, or soft logic. Discretionary dependencies are established based on knowledge of best practices within a particular application area or some unusual aspect of the project where a specific sequence is desired, even though there may be other acceptable
External dependencies.
External dependencies involve a relationship between project activities and non-project activities. These dependencies are usually outside the project team’s control.
Internal dependencies.
team’s control. Internal dependencies involve a precedence relationship between project activities and are generally inside the project
External Internal Mandatory Discretionary
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Leads or Lags
A lead is the amount of time whereby a successor activity can be advanced with respect to a predecessor activity. For example, on a project to construct a new office building, the landscaping could be scheduled to start two weeks prior to the scheduled punch list completion. This would be shown as a finish-to-start with a two-week lead.
SS + 15 Days(Lag)
A lag is the amount of time whereby a successor activity will be delayed with respect to a predecessor activity. For example, a technical writing team may begin editing the draft of a large document 15 days after they begin writing it. This can be shown as a start-to-start relationship with a 15-day lag.
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Precedence Diagramming Method
• • •
Visually easier to see precedence relationships Ideal for large projects with many activities They consist of a network of branches and nodes.
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Developing the Project Plan
•
The Project Network is a diagram that graphically depicts the sequence, interdependencies, and start and finish times of the project job plan of activities (tasks).
– – – – – –
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 can not be delayed.
–
Help managers get and stay on plan.
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Project Network Terminology
•
Activity:
–
an element of the project that requires time.
•
Merge Activity:
–
an activity that has two or more preceding activities on which it depends.
•
Parallel (Concurrent) Activities:
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Activities that can occur independently and, if desired, not at the same time.
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Project Network Terminology
•
Path: a sequence of connected, dependent activities.
•
Critical path: It is 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.
C+B+D=2+4 A+B+D=3+4 C B D A
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Basic Rules to Follow in Developing Project Networks
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 that is greater than any of its predecessor activities.
5. Looping is not allowed.
6. Conditional statements are not allowed.
7. Use common start and stop nodes.
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Project Network Terminology
•
Event: a point in time when an activity is started or completed. It does not consume time.
•
Burst Activity:
–
an activity that has more than one activity immediately following it (more than one dependency arrow flowing from it).
•
Two Approaches
–
Activity-on-Node (AON)
»
Uses a node to depict an activity.
–
Activity-on-Arrow (AOA)
»
Uses an arrow to depict an activity.
A
•
AON is the method used by most project management software packages.
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Activity-on-Arrow (AOA)
•
Identify the critical path
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Critical Path
•
Project Management Network Diagrams are helpful in determining where most of the schedule project risks (for project delay) will occur.
•
A critical path is made up of activities that cannot be delayed without delaying the end date of the project.
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Simple Example of Critical Path Method
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Create a List of Activity
Create the dependency diagram from the list above!
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Koll Business Center —Complete Network Sample
List all activities and connect them based on their dependencies.
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Koll Business Center —Complete Network
Indicate the duration (how many days) for each task. 6-9
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ES: Early Start
Project Activity Notations
ID EF: Early Finish SL: Slack or Float LS: Late Start Description: Activity Name Dur: Duration LF: Late Finish The activity ID and name The normal duration time (DUR) The early start time (ES) The early finish time (EF) The late start time (LS) The late finish time (LF) The slack http://en.wikipedia.org/wiki/Critical_path_method
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Network Computation Process
• •
Forward Pass —Earliest Times
– – –
How soon can the activity start? (early start —ES) How soon can the activity finish? (early finish —EF) Derive how soon can the whole project finish? (expected time —ET) Backward Pass —Latest Times
– –
How late can the activity start? (late start —LS) How late can the activity finish? (late finish —LF)
•
Calculate how long can activity be delayed? (slack or float —SL)
•
Identify critical paths (one or more) and which activities are on the critical path?
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Start from day 0
Forward Pass: Earliest Time
How soon can the project finish?
Early Start (ES) + Duration = Early Finish (EF ) or Early Start (ES) + Duration – 1 = Early Finish (EF) ES of an activity = the largest EF of its immediately preceding activities
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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 to be the ES of this activity.
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Latest day that the project should start
Backward Pass: Latest Time
Start here: The latest days that the project has to finish.
Late Finish (LF) - Duration = Late Start (LS) or Early Start (ES) + Duration = Early Finish (EF) LF of an activity = the smallest LS of its immediately successsor activities
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Backward Pass Computation
•
Use the EF of the last activity to be the LF of the last activity to get started.
•
Subtract activity times along each path in the network (LF - Duration = LS).
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Carry the late start (LS) to the next proceeding activity where it becomes its late finish (LF),
unless…
•
The next succeeding activity is a burst activity, in this case the smallest LS of all its intermediate successor activities is selected to establish its LF.
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Slack and Slippage
•
Now find the slack time (or 'float') for each task by subtracting the early start from the late start.
SL (Slack) = LS – ES Or substrcting early start from the late finish
•
SL (Slack) = LF – EF The slack time is the amount of time the task can be slipped by without affecting the end date of the process.
•
The critical path can now be identified as all paths through the network where the slack time is zero.
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Slippage: The amount of time that a task has been delayed from its original baseline plan. The slippage is the difference between the actual start or finish date for a task and the baseline (scheduled) start or finish date.
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Backward Pass with Slack
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Which path is the critical path?
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• • • •
Determining Free Slack (or Float)
Free Slack or just slack time: how much a task can slip before it delays another task.
–
It is the amount of time an activity can be delayed after the start of a longer parallel activity or activities.
–
It 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.
Total slack is how much a task can slip before it delays the whole project.
An activity on critical path has "zero free float", but activity that has zero free float might not be on the critical path.
Total float is associated with the path. The total float of a path is the combined free float values of all activities in a path.
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Sensitivity
•
Sensitivity
–
The likelihood the original critical path(s) will change once the project is initiated.
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The critical path is the network path(s) that has (have) the least slack in common.
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• • • • • • •
Develop Schedule: Tools and Techniques
Schedule Network Analysis Critical Path Method Critical Chain Method Resource Leveling What-if Scenario Analysis Applying Leads and Lags / Laddering Schedule Compression Techniques:
–
Crashing the critical path
(i.e., shortening the durations of critical path activities by adding resources).
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Fast tracking
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Critical Path Method (CPM)
•
In project management, a critical path is the sequence of project network activities which add up to the longest overall duration.
•
This determines the shortest time possible to complete the project.
•
Any delay of an activity on the critical path directly impacts the planned project completion date i.e. there is no float (slack) on the critical path.
•
A project can have several, parallel, near critical paths.
http://en.wikipedia.org/wiki/Critical_path_method
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Critical Path Analysis
• • •
What tasks must be carried out.
Where parallel activity can be performed.
The shortest time in which you can complete a project.
• • • •
Resources needed to execute a project.
The sequence of activities, scheduling and timings involved.
Task priorities.
The most efficient way of shortening time on urgent projects.
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Critical Path Analysis
• • •
Regularly view the critical path(s).
Closely monitor critical tasks.
Review series of tasks that may become part of the critical path.
•
Protect yourself by examing tasks that can slip without affecting the critical path.
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PERT (Program Evaluation and Review Technique)
• •
PERT is a variation on Critical Path Analysis that takes a slightly more skeptical view of time estimates made for each project stage. To use it, estimate the shortest possible time each activity will take, the most likely length of time, and the longest time that might be taken if the activity takes longer than expected.
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Three-Point Estimates
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CPM vs. PERT
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CPM or "Critical Path Method":
–
A single estimate for activity time was used that did not allow for variation in activity times
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Activity times are assumed to be known or predictable ("deterministic")
•
PERT (Project Evaluation and Review Technique)
–
Multiple time estimates were used for each activity that allowed for variation in activity times
–
Activity times are assumed to be random, with assumed probability distribution ("probabilistic")
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How to Create a Schedule from a Precedence Diagram
Resource
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Practical Considerations
•
Network logic errors
•
Activity numbering
•
Use of computers to develop networks
•
Calendar dates
•
Multiple starts and multiple projects
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Accelerating Project Completion
•
When resources are not constrained
– – – – –
Add resources Outsource some project work Schedule overtime Establish a core project team Do it twice (quick prototype to get by and than the real one)
•
When resources are constrained
–
Fast-tracking
– –
Reduce project scope Compromise quality (rarely used)
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Schedule Compression Techniques
•
Crashing:
A technique used to shorten the schedule duration for the least incremental cost by adding resources. Examples of crashing include approving overtime,
bringing in additional resources
, or paying to expedite delivery to activities on the critical path. Crashing works only for activities on the critical path where additional resources will shorten the activity’s duration. Crashing does not always produce a viable alternative and may
result in increased risk and/or cost
.
•
Fast tracking.
A schedule compression technique in which activities or phases normally done in sequence are
performed in parallel
for at least a portion of their duration. An example is constructing the foundation for a building before completing all of the architectural drawings. Fast tracking may
result in rework and increased risk
. Fast tracking only works if activities can be overlapped (even partially overlapped) to shorten the project duration.
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Extended Network Techniques
• •
Laddering (further decomposition)
–
Activities are broken into segments so the following activity can begin sooner and not delay the work.
Lags
–
The minimum amount of 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.
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Use of Lags
Finish-to-Start Relationship Start-to-Start Relationship PM: Scheduling - 56
Precedence Diagramming Method
• • •
The project management team determines the dependencies that may require a lead or a lag to accurately define the logical relationship.
A lead allows an acceleration of the successor activity. A lag directs a delay in the successor activity.
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Use Lead or Lag to Create Partially Parallel Tasks
•
Fast Tracking Overlapped Overlapped SS + 15 Days (Lag) Lead Time - is an acceleration of the successor activity
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Hammock Activities
• •
An activity that spans over a segment of a project. Duration of hammock activities is determined after the network plan is drawn.
Hammock activities (summary activity) are used to aggregate sections of the project to facilitate getting the right amount of detail for specific sections of a project.
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Hammock Activity
A hammock activity can group tasks which are not related in the hierarchical sense of a Work Breakdown Structure, or are not related in a logical sense of a task dependency where one task must wait for another. Usages include: • Group dissimilar activities that lead to an overall capability, such as preparations under a summary label, e.g. "vacation preparation"; • Group unrelated items for the purpose of a summary such as a calendar-based reporting period, e.g. "First quarter plans"; • Group ongoing or overhead activities that run the length of an effort, e.g. "project management" ©
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Avoid Linking Summary Tasks
It generally is not recommended to use links on summary activities because the logic can be difficult to follow and the practice may not be supported by all scheduling tools. Use of links on summary activities may produce logic errors and create circular logic within the schedule model.
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Resource Leveling and Resource Smoothing
http://www.izenbridge.com/blog/underlining-the-differences between-resource-leveling-and-resource-smoothing/
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Resource Leveling
• A technique in which start and finish dates are adjusted based on resource constraints with the goal of balancing demand for resources with the available supply. • • Resource leveling can be used when shared or
critically required resources
are only available at certain times, or in limited quantities, or over allocated, such as when a resource has been assigned to two or more activities during the same time period or to keep resource usage at a constant level.
Resource leveling can often cause the original critical path to change, usually to increase
.
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Resource Smoothing
• A technique that adjusts the activities of a schedule model such that the requirements for resources on the project do not exceed certain predefined resource limits. •
In resource smoothing
, as opposed to resource leveling,
the project’s critical path is not changed and the completion date may not be delayed
. • In other words,
activities may only be delayed within their free and total float
resources.
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Key Terms
Activity Activity-on-arrow (AOA) Activity-on-node (AON) Burst activity Concurrent engineering Critical path Early and late times Gantt chart Hammock activity Lag and Lead relationship Merge activity Network sensitivity Parallel activity Slack/float —total and free
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Free Float vs. Total Float
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Extra
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Critical Chain Method
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• • • •
Critical Chain Method
The resource-constrained critical path is known as the critical chain. The critical chain method adds duration buffers that are non-work schedule activities to manage uncertainty. One buffer, placed at the end of the critical chain, is known as the project buffer and protects the target finish date from slippage along the critical chain. Additional buffers, known as feeding buffers, are placed at each point that a chain of dependent tasks not on the critical chain feeds into the critical chain. Feeding buffers thus protect the critical chain from slippage along the feeding chains. The size of each buffer should account for the uncertainty in the duration of the chain of dependent tasks leading up to that buffer. Once the buffer schedule activities are determined, the planned activities are scheduled to their latest possible planned start and finish dates. Consequently, in lieu of managing the total float of network paths, the critical chain method focuses on managing remaining buffer durations against the remaining durations of task chains.
Ref: http://en.wikipedia.org/wiki/Critical_chain_project_management
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