1 540f07cost10 Question of the Day u How important is it to be able to estimate the cost of a software project?

2 540f07cost10 exam preview – 150 pts – 10/11/07 1. (30 pts) requirements create scenarios for a problem 2. (30 pts) PERT diagrams 3. (20 pts) Cost Estimation 4. (40 pts) definitions and short discussions 5. (30 pts) 10 multiple choice One crib sheet (8.5 by 11, handwritten) allowed, turn in with exam

3 540f07cost10 PERT Diagrams u Program Evaluation and Review Technique a1 a2 a3 a4 a5

4 540f07cost10 Critical Path u If there are N tasks with dependencies between the tasks, what set of tasks determines the minimum completion time for the whole project? u This is the critical path.

5 540f07cost10 Critical Path Algorithm (part 1) u For each node (until completion time of all nodes are calculated) »if the predecessors are completed, then take latest completions time and add required time for this node; »this is the completion time. u The node with the latest completion time determines the earliest completion time for project.

6 540f07cost10 Example

7 540f07cost10 Critical Path Algorithm (part 2) u Starting with the node with latest completion time, mark it as critical. u Select predecessor node with latest completion time, mark it as critical. u Continue until reaching start node.

8 540f07cost10 Example

9 540f07cost10 Critical Path Algorithm (part 3) u Slack time is the amount of time that a specific task can be delayed without changing the project delivery time u For each noncritical node starting with the last node, determine the earliest of the latest start times of the successor nodes. This is the latest completion time. Make the latest start time for the node to reflect this time.

10 540f07cost10 Example

11 540f07cost10 TTYP

12 540f07cost10 Cost Estimation An estimate of the effort and duration, associated costs of equipment, travel and training and the rationale for the calculations

13 540f07cost10 Recommendation u If you are involved with cost estimation, I recommend the following book u Tom DeMarco, Controlling Software Projects, Yourdon Press, NY c1982

14 540f07cost10 Definition of Estimate (DeMarco) u Default: – "An estimate is the most optimistic prediction that has a non-zero probability of coming true" u Proposed: – "An estimate is a prediction that is equally likely to be above or below the actual result"

15 540f07cost10 Estimates should not become goals u DeMarco argues that the estimation and the management decision about pricing or goals should be separate.

16 540f07cost10 Estimate

17 540f07cost10 Cost Estimate u should not be a contract bid u should not be a schedule u should be input into the management decision to determine the above u should be re-estimated frequently

18 540f07cost10 TTYP1 u Given the following data, what would be your estimate for a project that would be about 200K? What would you use for a cost estimation formula? u Historical data –project 1 100K50 prog-months –project 220K10 prog-months –project 314K7 prog-months –project 416K8 prog-months

19 540f07cost10 Confidence in your estimate u How confidence are you in this estimate? u Would you stake your job/grade on this estimate? u What would be your concerns? u What could you do to increase your confidence? u What would you consider to be a successful estimate?

20 540f07cost10 Problems u Programmer variability u Product complexity u Variability of goal u Conflict of goals u Lack of detailed product description u Variation in effort to reuse code u Emergence of new processes, methods and tools

21 540f07cost10 Cost Estimation Models u LOC models – Boehm's COCOMO – Price S – Putnam's Model (SLIM) u non-LOC models – Function Points u combination – COCOMO2

22 540f07cost10 Prediction Formulas E=  X    >1  <1  =1 TTYP2 – which one did Henry Ford experience? Which one happens in your project? Size cost A non-zero gamma would shift line up or down

23 540f07cost10 Tuesday, 10/2 Read SOS section 4.4.3