Presentation on theme: "Scheduling Work I love deadlines. I love the sound they make as they fly by. -- Douglas Adams."— Presentation transcript:
Scheduling Work I love deadlines. I love the sound they make as they fly by. -- Douglas Adams
What is the purpose of a project schedule? 1. Coordinate What to do and When? 2. Monitor Are we on time? Are problems starting to occur?
Reminder: Why is software late? Under-Estimate of effort. Unrealistic deadlines imposed by outsiders. Changing requirements. Risks that were not considered. Technical problems that could not be foreseen. Failure to recognized that the project is falling behind schedule and lack of action to correct the problem. Software Engineering : A Practitioners Approach by Pressman
How to build a schedule (which you already learned in CSCI 475/476) 1. Determine dependencies of activities. Major Activities are listed in the WBS. Leverage past projects to determine dependencies. Surprises are very bad. 2. Use dependencies to build activity network diagram (e.g. PERT chart). 3. Determine critical path. 4. Map network to a timeline (e.g. Gantt chart) using the effort estimates. Use a software tool to help do this work.
Dependency Types External Dependency Other projects Stakeholders Sub-Contractors Internal Dependency Audits (design, testing, documentation, …) Sign-Offs at end of phase
Dependency Types S tart F inish FS - T2 cannot start until T1 is finished. coding must wait on design to be finished SS - T1 and T2 must start at same time. documentation and coding start together FF - T1 and T2 finish at same time. configuration management ends when testing is done
Dependency Types Lag – T2 cannot start until a given amount of time after T1 is done. Start on-site training one week after final demo to customer management group. Soft – T2 should start after T1, but it is not completely essential that T1 be finished. Populate the new database after the database has been built. If the new database is not completely finished we can still populate the few finished tables.
Activity Networks CPM – Critical Path Method activities are graph nodes (circles or squares) single estimate for duration of tasks PERT – Program Evaluation and Review Technique activities are graph arcs (lines) activity times are ranges and include probabilities
http://www.cs.unc.edu/~stotts/COMP145/homes/map/images/pert.gif CPM Example
http://www.mckinnonsc.vic.edu.au/la/it/ipmnotes/ganttpert/pert_chart.gif PERT Example
Example Activity Network – Activity on Node T1 T2 T3 T4T6 T5 T7 T8T9 1wk 2wks 4wks 3wks 1wks 1wk 3wks 2wks1wk Questions: 1. Minimum time to complete the project? 2. Critical Path? 3. For T2, what are the earliest start time, latest start, earliest finish, latest finish? es=2 nd wk ls=4 th wk ef=3 rd wk lf=5 th wk
Advanced Scheduling Topics Using Milestones Managing Uncertainty in the Timeline PERT confusion Resource Leveling Using Scheduling Tools
Milestones Why must you schedule milestones, such as reviews, throughout the project?
Managing Uncertainty Q: Q: How confident can we be in our milestone dates and the delivery date? Q: Q: Can we calculate the confidence level? A: A: Using confidence values and Statistics 1.for each task, determine pessimistic and optimistic times 2.if PT-OT is small for all tasks, then great!!! 3.compute average PT-OT, and std dev 4.if a task's PT-OT is outside the std dev, worry about that task
Managing Uncertainty Q: Where do we schedule uncertainty time? A1: spread it out by bumping each milestone. used by Critical Path A2: lump it together as one activity at end. used by Critical Chain
Common PERT Problem K – integration testing L – Install Software M – Write Manual N – Train Users But wait, we can shorten the project if we write the manual right after testing is finished. (L and M can be done in parallel.) So… 34521 K L MN
Pert Problem cont… K – integration testing L – Install Software M – Write Manual N – Train Users But wait, the system needs to be installed before we can use it to train people. So… 3 45 21 K L M N
Pert Problem cont… K – integration testing L – Install Software M – Write Manual N – Train Users But what is that activity between dates 3 and 4? So… 3 4 5 21 K L M N
Pert Problem cont… K – integration testing L – Install Software M – Write Manual N – Train Users Dashed line is a dummy activity. 3 4 5 21 K L M N
Pert Problem cont… Note: dummies not needed with "activity on node" graphs. K N M L K – integration testing L – Install Software M – Write Manual N – Train Users
Resource Leveling Leveling usually yields longer projects Activity Shifting to avoid using resources during a peak time. use slack in start and end dates Activity Splitting to shorten duration break long activity into pieces when more resources are available Optimize the System, not individual tasks
Leveling Example What is the completion time? Since F is so long, what would be the completion time if we break F into two parallel parts of 2wks and 3wks? A 3wks B 2wk E 2wks C 2wks F 5wks G 3wks H 3wks I 2wks D 2wks
Scheduling Tools Gantt Chart producers MS Project Web access Supports multiple projects Dependencies Billing support Resources leveling Gantt charts, activity network, …