1. 5 th LectureCEN 4021: Software Engineering II Task Sequence and Effort representation  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

2. 5 th LectureCEN 4021: Software Engineering II Task sequence/effort table TaskImmediate prerequisite tasks Effort (person-days) ANone9 BA5 CA7 DB,C11 ED8 Total effort required: 40 person-days

3. 5 th LectureCEN 4021: Software Engineering II Graphical representation of tasks from previous table Task A Task B Task C Task D Task E End Critical Task Non-critical Task Critical Path Non-critical Path 9 9 5 7 118 Total project time: 35 days

4. 5 th LectureCEN 4021: Software Engineering II Critical versus Non-Critical Paths 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.

5. 5 th LectureCEN 4021: Software Engineering II 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.

6. 5 th LectureCEN 4021: Software Engineering II Task Scheduling  Forward-pass scheduling –Early start time (ES) and early finish (EF)  Backward-pass scheduling –Late start (LS) and Late finish (LF)  Slack time

7. 5 th LectureCEN 4021: Software Engineering II Forward-pass scheduling TaskTasks precedence Task lengthEarliest possible start time (ES) Earliest possible finish time (EF) ANone90 BA5 CA7 DB,C11 ED8 9 914 916 27 35

8. 5 th LectureCEN 4021: Software Engineering II Backward-pass scheduling TaskTasks precedence Task lengthLate start time (ES) Late finish time (EF) ANone9 BA5 CA7 DB,C11 ED8 9 16 9 27 35 0

9. 5 th LectureCEN 4021: Software Engineering II Slack 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 - ES Or Total slack time of a task = LF – EF e.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.

10. 5 th LectureCEN 4021: Software Engineering II Program Evaluation and 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.

11. 5 th LectureCEN 4021: Software Engineering II Program Evaluation and Review Technique (PERT) Expected estimate (EE) = [O + P + (4 x A)] / 6 Where O = most optimistic estimate P = most pessimistic estimate A = most likely estimate

12. 5 th LectureCEN 4021: Software Engineering II Program Evaluation and Review Technique (PERT) Expected Project time (EPT)  Sum of expected estimates of the critical tasks. EPT = Σ(EE of all critical task)

13. 5 th LectureCEN 4021: Software Engineering II CPM 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