Post on 17-Jan-2018
description
5th LectureCEN 4021: Software Engineering II
Task Sequence and Effort Task Sequence and Effort representationrepresentation
All tasks share at least two basic characteristics– Require effort in terms of person-days required to complete
each task
– A specified order for processing the task
5th LectureCEN 4021: Software Engineering II
Task sequence/effort tableTask sequence/effort table
Task Immediate prerequisite
tasks
Effort (person-days)
A None 9
B A 5
C A 7
D B,C 11
E D 8
Total effort required: 40 person-days
5th LectureCEN 4021: Software Engineering II
Graphical representation Graphical representation of tasks from previous of tasks from previous tabletable
Task A
Task B
Task C
Task D
Task E
End
Critical Task
Non-critical Task
Critical Path
Non-critical Path
9
9 5
7
11 8
Total project time: 35 days
5th LectureCEN 4021: Software Engineering II
Critical versus Non-Critical Critical versus Non-Critical PathsPaths
Critical path The path that takes the most time to complete.
Critical task (critical activity) A task that resides on the critical path.
Non-critical path Any path that is not a critical path and thus takes less effort to complete
than the critical path.
Non-critical task (non-critical activity) Any activity that resides on a non-critical path and not a critical path.
These tasks may accept some delay in completion.
5th LectureCEN 4021: Software Engineering II
Critical Path Method (CPM)Critical Path Method (CPM)“The critical path method analyses the precedence of
activities to predict the total project duration. The method calculates which sequence activities (path) has the least amount of flexibility ”– Quality Software Project Management, Futrell et. al.
5th LectureCEN 4021: Software Engineering II
Task SchedulingTask Scheduling Forward-pass scheduling
– Early start time (ES) and early finish (EF)
Backward-pass scheduling– Late start (LS) and Late finish (LF)
Slack time
5th LectureCEN 4021: Software Engineering II
Forward-pass schedulingForward-pass scheduling
Task Tasks precedence
Task length Earliest possible start time
(ES)
Earliest possible
finish time (EF)
A None 9 0
B A 5
C A 7
D B,C 11
E D 8
9
9 14
9 16
16 27
27 35
5th LectureCEN 4021: Software Engineering II
Backward-pass schedulingBackward-pass scheduling
Task Tasks precedence
Task length Late start time (ES)
Late finish time (EF)
A None 9
B A 5
C A 7
D B,C 11
E D 8
9
11 16
9 16
16 27
27 35
0
5th LectureCEN 4021: Software Engineering II
Slack timeSlack time
Total slack time of an activity– The difference in start time between a non-critical task’s late
start time and its early start time or its late finish time and early finish time.
Total slack time of a task = LS - ESOrTotal slack time of a task = LF – EFe.g., Activity B: LS – ES (11 - 9) or LF – EF (16 - 14) => 2
Total slack time– The maximum allowable delay for all non-critical activities.
5th LectureCEN 4021: Software Engineering II
Program Evaluation and Program Evaluation and Review Technique (PERT)Review Technique (PERT)
An estimating technique assumes each activity duration is subject to a range
estimates uses weighting method to arrive at a specific duration.
5th LectureCEN 4021: Software Engineering II
Program Evaluation and Program Evaluation and Review Technique (PERT)Review Technique (PERT)
Expected estimate (EE) = [O + P + (4 x A)] / 6
WhereO = most optimistic estimateP = most pessimistic estimateA = most likely estimate
5th LectureCEN 4021: Software Engineering II
Program Evaluation and Program Evaluation and Review Technique (PERT)Review Technique (PERT)
Expected Project time (EPT) Sum of expected estimates of the critical tasks.EPT = Σ(EE of all critical task)
5th LectureCEN 4021: Software Engineering II
CPM vs PERTCPM vs PERT Scheduling a lot of activities with 3 estimates
computationally messy many people argue 3 estimates are not much more
accurate than 1 estimate Most project management scheduling software use CPM