A big challenge facing iterative projects is to estimate what work efforts shoul

Question

A big challenge facing iterative projects is to estimate what work efforts should be undertaken in individual iterations. One approach to estimating work efforts per iteration is to start by creating a rough PERT/CPM chart that lays out your best understanding of what needs to be done on the project. It is important that the PERT/CPM chart show both tasks and resulting milestones, where milestones reflect executable code.

The PERT/CPM chart below shows task sequences and durations associated with a hypothetical project. Using the information contained in the PERT/CPM chart:

a) Calculate the critical path;

b) Calculate latest and earliest start dates for each task and milestone;

c) Calculate float for each task.

Assuming the target length of iteration is about 4 weeks (20 days if you ignore weekends), identify how you would organize the tasks by iteration. Assume you have all the resources you need. Explain how working with known resource constraints would affect how you carry out this exercise.

Milestone X Executable Code Task A 7 days duration A-7d MS- Earliest start Float Earliest Latest Latest start MS-A MS-E A-7d B-5d C-6d -10d MS-B D-6d E-6d H-7d J-8d K-13d Start End MS-C MS-D MS-F F-15d G-13d L-4d M-6d N-4d Estimating Work Efforts Assigned to Each lteration of a Project

Explanation / Answer

a) Critical path is the path of longest duration in the network.

Critical path is A-B-C-(MS-A)-H-J-K-(MS-E)

Completion time = 46 d

Answer to b) and c) follows:

Draw the table listing ES, LS, EF, LF and Slack of each activity as below:

Earliest Start is calculated by forward pass method as latest of the predecessors Earliest Finish.

Latest Finish is calculated using backward pass method as earliest of the successors Latest Start.

Earliest Finish = Earliest Start + Activity Duration

Latest Start= Latest Finish - Activity Duration

Slack = Latest Finish - Earliest Finish, or Latest Start - Earliest Start

Activity Duration Earliest Start Latest Start Earliest Finish Latest Finish Slack Critical Activity A 7 0 0 7 7 0 Critical B 5 7 7 12 12 0 Critical C 6 12 12 18 18 0 Critical MS-A 0 18 18 18 18 0 Critical D 6 0 1 6 7 1 E 6 6 12 12 18 6 MS-B 0 12 18 12 18 6 F 15 0 4 15 19 4 G 13 15 19 28 32 4 MS-C 0 28 32 28 32 4 H 7 18 18 25 25 0 Critical I 10 25 36 35 46 11 J 8 25 25 33 33 0 Critical K 13 33 33 46 46 0 Critical MS-E 0 46 46 46 46 0 Critical L 4 28 32 32 36 4 MS-D 0 32 36 32 36 4 M 6 32 36 38 42 4 N 4 38 42 42 46 4 MS-F 0 42 46 42 46 4

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