2001ict Mo8 Lec
Transcript of 2001ict Mo8 Lec
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2001ICT - Project Management
Module 8 1
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2001ICT - Project
Management
Module 8
Building Schedule
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Reading
Schwalbe Chapters 6
PMBOK Chapter 6
Burrill & Ellsworth Chapters 15 & 16
Cotterell & Hughes Chapters 6 & 8
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Review
Software Life Cycle Model
Waterfall, Prototyping, Evolutionary ...
Work Breakdown Structure
Based upon defined process model
Activity Network Diagram
Estimation Principles Functional Size Measurement
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Module Outline
What is Time Management
Time Management Processes
Network Diagrams
Critical Paths
Schedule Management and Control
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Project Time Management
Project Time Management includes theprocesses required to ensure timely completionof the project.
These processes interact with each other andwith the processes in the other knowledge areasas well.
Each process may involve effort from one ormore individuals or groups of individuals based
on the needs of the project. Each process generally occurs at least once in
each phase of the project.
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Managing Project Time
ActivityDefinition
ActivitySequencing
ScheduleDevelopment
ScheduleControl
ActivityDuration
Estimating
ActivityResource
Estimating
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Time Management Processes
Activity Definitionidentifying the specific activities that mustbe performed to produce the various project deliverables.
Activity Sequencingidentifying and documenting interactivitydependencies.
Activity Resource Estimating - estimating how manyresources a project team should use to perform projectactivities.
Activity Duration Estimatingestimating the number of workperiods which will be needed to complete individual activities.
Schedule Developmentanalyzing activity sequences,
activity durations, and resource requirements to create theproject schedule.
Schedule Controlcontrolling changes to the projectschedule.
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Activity DefinitionWork breakdown structure
Scope statement
Historical information
Constraints
Assumptions
Expert Judgement
Activity list
Supporting detail
Work breakdown structure updates
ActivityDefinition
Activity definition involves identifyingand documenting the specific activitiesthat must be performed in order toproduce the deliverables and sub-deliverables identified in the workbreakdown structure.
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Activity Definition
Tools and Techniques Decomposition
Essentially the same as in Scope Definition
The major difference is that this
decomposition results in outputs described as
activitiesrather than as deliverables.
The WBS and the Activity List are usually
developed sequentially:
The WBS is the basis for development of the
final activity list.
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Activity SequencingActivity list
Product description
Mandatory dependencies
Discretionary dependencies
External dependencies
Milestones
Project network diagrams
Activity list updates
ActivitySequencing
Activity sequencing involves identifying anddocumenting interactivity logical relationships.
Activity must be sequenced accurately to supportlater development of a realistic and achievableschedule.
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Ordering Tasks
WBS Element Input Output
Task T A B
Sub-task T1 A W
Sub-task T2 W X
Sub-task T3 X Y
Sub-task T4 W Z
Sub-task T5 Y, Z B
T1 T2 T3 T4 T5A B
T1
T2T3
T4 T5
A B
Sequential Ordering
Non-sequential Ordering
T1 T2 T3 T4 T5
T
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Representing an Activity
Network Precedence diagramming method
Nodes represent the Activities
Connections show thedependencies
Arrow diagramming method Arrows represent the activities
Connections at the nodes showdependencies
Conditional diagramming methods Allow for non-sequential activities
(such as loops)
A B C
D E F
Start
A
B
C
D
EF
Finish
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The Activity Network Diagram
The Activity Network Diagram is the end-product
of the task decomposition process
It should be accompanied by narrative to explain any
dependencies
It shows the relationships between the tasks that
have to be performed, but says nothing about
how long it will take to perform them
To go further we need to be able to estimatethe
effort, cost and elapsed time for each task or activity
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Activity Resource Estimating
Before estimating activity durations, you musthave a good idea of the quantity and type ofresources that will be assigned to each activity.
Consider important issues in estimatingresources:
How difficult will it be to complete specific activities onthis project?
What is the organizations history in doing similaractivities?
Are the required resources available?
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Activity Duration EstimatingActivity list
Constraints
Assumptions
Resource requirements
Resource capabilities
Historical information
Identified risks
Activity duration estimates
Basis of estimates
Activity list updates
Activity DurationEstimating
Activity duration estimating isthe process of taking informationon the project scope andresources and then developingdurations for input to schedules.
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Estimate Activity Duration
You need to estimate how long it will take tocomplete each activity in the Activity List.
The relationship between effort estimates and
elapsed time is not simple. Calendars, number of personnel, availability of other
resources influence the duration
Use historical data as the basis for estimationwherever possible.
Techniques include: Expert judgment
Analogous estimation
Simulation
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Schedule DevelopmentProject network diagrams
Activity duration estimates
Resource requirements
Resource pool description
Calendars
Constraints
Assumptions
Leads and lags
Risk management planActivity attributes
Project Schedule
Supporting detail
Schedule management plan
Resource requirement updates
ScheduleDevelopment
Schedule development means determining startand finish dates for project activities. If the startand finish dates are not realistic, then the projectis unlikely to be finished as scheduled.
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Techniques for Scheduling
Mathematical Analysis Critical Path Method (CPM)
uses single deterministic early and late start and finish dates
for each activity Program Evaluation and Review Technique (PERT)
uses sequential network logic and weighted average durationestimates to calculate project duration
Duration Compression ways to shorten the schedule without changing the
scope
Resource Levelling Heuristics
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Paths in Networks
A path is a sequence of activities that starts with abeginning activity and travels through a series ofimmediate successors until it terminates with an endingactivity
The length of a path is the total time it takes to traversethe path; that is, the total of the durations for theactivities on the path
For any network there is a maximum to the lengths of allthe paths through the network.
Any path whose length is equal to this maximum iscalled a critical path Note that there may be more than one critical paths in a network.
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Calculating the Critical Path
We use a Network
Diagram and label the
nodes to show: Task duration;
Early finish time;
Late finish time;
Slack
ID
S
Slack
LF
Late Finish
EF
Early Finish
D
Duration
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Critical Path Method - 1
Calculate Early Start and EarlyFinish Times
The ES for an activity is themaximum of the EF times forall of its immediatepredecessors
The ES for the beginningactivity (I.e. with nopredecessors) is 0.
For each activity, the EF is
equal to the ES plus theduration
Assigning ES and EF timesinvolves making a forwardpassthrough the network.
Activity Duration
A 2
B 4
C 5
D 4
E 6
F 3
2 4 5
4 6 3
2 6
4 10 13
11
130
A B C
D E F
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Critical Path Method - 2
Calculate Late Start and LateFinish Times
For each activity, the LS is equalto the LF minus the duration
The LF for the ending activity(I.e. with no successors) is thesame as the EF, unless theduration for the entire network isknown.
The LF for an activity is theminimum of the LS times for all ofits immediate successors
Assigning LS and LF timesinvolves making a backward passthrough the network.
Activity Duration
A 2
B 4
C 5
D 4
E 6
F 3
2 4 5
4 6 3
2 6
4 10 13
11
13013
13104
84
A B C
D E F
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Critical Path Method - 3
Calculate Slack
For each activity, the Slack isequal to the Late Finish minusthe Early Finish
(also, Slack - LS - ES)
The slack of an activity is theduration that the activity canbe delayed without delayingthe project, providing it is theonly activity delayed.
Activities that have theminimumslack are those onthe critical path.
Activity Duration
A 2
B 4
C 5
D 4
E 6
F 3
2 4 5
4 6 3
2 6
4 10 13
11
130
13
13104
842
000
2 2
A B C
D E F
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Why critical paths are important
Slippage of an activity on a critical path results inslippage of the project completion date.
Improvement of the total project duration is most
responsive to improvements along a critical path. It is possible to lengthen non-critical activities without
adverse effect on the project duration.
Critical activities are the ones most in need ofmanagement attention, since their delay most impactsthe project.
Note: the activities on the critical path are not necessarilythe most important activities in the project!
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Alternative Dependencies
The standard Critical Path Method is based on simplefinish - start dependencies - ie one task must end beforeanother can begin
Other more complex dependencies are possible: Start to start - one activity cannot start until another starts
End to end - one activity must finish before another can finish
Start to end - one activity must start before another can finish
In each case, it is also possible to identify laggeddependencies.
e.g. Task A cannot start until a specified time after Task Bfinishes.
Good Scheduling Tools allow all of these dependenciesto be recognised.
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Tools for schedule management
Microsoft Project - Gantt Chart
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Tools for schedule management
Microsoft Project - PERT Network
Task A
Start: 4/09/06 ID : 2
F ini sh :5/ 09 /06 D ur : 2d ays
Res:
Task B
Start: 6/09/06 ID: 3
F in ish :11 /0 9/ 06 D ur : 4 da ys
Res:
Task C
Start: 12/09/06 ID: 4
F in ish : 18 /0 9/ 06 D ur : 5 da ys
Res:
Task D
Start: 4/09/06 ID : 5
F ini sh :7/ 09 /06 D ur : 4d ays
Res:
Start
Milestone Date:Mon 4/09/06
ID :1
Task E
Start: 8/09/06 ID: 6
F in ish :15 /0 9/ 06 D ur : 6 da ys
Res:
Task F
Start: 18/09/06 ID: 7
F in ish : 20 /0 9/ 06 D ur : 3 da ys
Res:
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Resource Allocation
Two factors have to be considered in the
allocation of resources:
the resource requirements - the duration of mosttasks is significantly affected by the resources
assigned
the resource capabilities - the duration of most
activities is influenced by the capabilities of the
people assigned to them.
Normally, resources are allocated at the same
time as the network is constructed.
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Resource Limitations
The calculation of critical path assumes
that resources are not constrained.
In the real world constraints always exist.
0
1
23
4
5
6
7
1/01/00 1/02/00 1/03/00
Time
Projec
tStaffing
Theory
Practice
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Levelling the Project
Different strategies are available to deal
with resource constraints:
Levelling by adjusting Levelling by replanning
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Resource levelling -
an example (1)
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Resource levelling -
an example (2)
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Schedule ControlProject schedule
Performance reports
Change requests
Schedule management plan
Schedule updates
Corrective action
Lesson learned
ScheduleControl
Schedule control is concerned witha) influencing the factors that create schedule
changes to ensure that changes are agreed upon,b) determining that the schedule has changed, andc) managing the actual changes when and as they
occur.
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Controlling the Schedule
How does a project
get to be six months
late?
Fred Brooks
The Mythical Man Month
One day at a time!
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Adjusting the Schedule
Several strategies are available to help
meet constraints on resources:
Extending the project
Slipping activities
Splitting Activities
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Extending the Project
May be the rational response to resourceconstraints
Requires firm credibility in the estimates Move from treating estimation as a political
activity to seeing it as a necessarytechnical task
Even if the project cannot be extended,the arguments may result in moreresources being made available.
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Slipping Activities
General heuristics are available to support scheduleadjustment to meet resource constraints
When slipping activities, start by making use of the slackperiods the difference between slack and float can be important
float is the amount of flexibility in scheduling an activity that willnot affect any other activity
slack also includes adjustments that impact on other activities,but do not affect the overall project duration
If you have to slip activities that are on the critical path,then the overall completion date will be affected
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Choosing the Slippage
How do you choose between several tasks for slippage? ES, EF, LS or LF
Duration
An assigned priority Responsible department
Subnetwork membership
Random selection
Slip activities at random and generate several differentschedules meeting the resource constraints
Select the one that offers the best completion date!
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Splitting Activities
Start an activity and pause before
completion
Return and complete the activity when
resources are available
Note that some activities cannot be split!
Splitting tends to confuse people There are overheads associated with
picking up the loose threads
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Replanning the Project
Replan the Activities
re-assign resources
make effective use of resources when thereare surplus
Replan the Network
re-examine the dependencies
it may be possible to perform tasks in parallel
rather than in series
take advantage of partial dependencies
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Compressing the Duration
Techniques for duration compression include:
Crashing - analyse cost and schedule trade-offs to
determine how to obtain the greatest compression for
the least incremental cost.
There is not always a viable alternative.
Crashing often results in increased costs.
Fast tracking - performing activities in parallel that
would normally be done in sequence. Start coding before the design is complete
Often results in increased rework
Usually increases risk
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Summary - 1
Starting from the WBS and individual task estimates, we can build anetwork and assign durations to the tasks in the network.
There will usually be a number of different paths through anynetwork. We can calculate the duration of any path; there will
always be a maximum duration for any network. Paths which take this maximum duration are called critical paths Any schedule contains not only the activities and their durations, but
also the identified resources required.
The process of adjusting a schedule to meet resource constraints iscalled resource levelling.
Controlling the schedule may involve a variety of strategies: Extending the project
Slipping activities
Splitting activities
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Exercise
What are the processes involved in Time
Management?
What steps do you use to develop a
schedule?
What is a critical path? Why is it
important?