Make or Buy Algorithm Makeor Buy Example Assume

Make or Buy Algorithm

Make-or Buy Example Assume you can lease an item you need for a project for $150/day. To purchase the item, the investment cost is $1, 000, and the daily cost would be another $50/day. How long will it take for the lease cost to be the same as the purchase cost? If you need the item for 12 days, should you lease it or purchase it? 2

Make-or Buy Solution Set up an equation so the “make” is equal to the “buy” In this example, use the following equation. Let d be the number of days to use the item. $150 d = $1, 000 + $50 d Solve for d as follows: Subtract $50 d from the right side of the equation to get $100 d = $1, 000 Divide both sides of the equation by $100 d = 10 days The lease cost is the same as the purchase cost at 10 days If you need the item for 12 days, it would be more economical to purchase it 3

Part 2: Integration and System Testing

A Big-Bang Approach B Test A Test B E Test C Test D Test E Test F Test G Test A, B, C, D, E, F, G C F D G

A Bottom-up Integration B Test E E Test B, E, F Test C Test G Test D, G Test A, B, C, D, E, F, G C F D G

A Top-down Integration B E C F Test A, B, C, D, E, F, G Layer I + II All Layers D G

A Sandwich Testing Strategy B C D Test A E Test A, B, C, D Test B, E, F Test D, G Test G G F Test A, B, C, D, E, F, G

A Modified Sandwich Testing B C D Test A, C Test C E F Test B Test E Test B, E, F Test D, G Test A, B, C, D, E, F, G G

Managing Systems Projects 10

Estimating Task Completion Time and Cost Task completion times and related cost estimates usually are expressed in person-days that represent the amount of work that one person can complete in one day. For example: if it will take one person 20 days to perform a particular task, it might not be true that two people could complete the same task in 10 days or that 10 people could perform the task in two days. In most systems analysis tasks, however, time and people are not interchangeable. If one analyst needs two hours to interview a user, two analysts also will need two hours to do the same interview. Slide 11

Estimating Task Completion Time and Cost Project managers often use a weighted formula for estimating the duration of each task. The project manager first makes three time estimates for each task: an optimistic, or best-case estimate (B), a probable-case estimate (P), and a pessimistic, or worst-case estimate (W) The manager then assigns a weight, which is an importance value, to each estimate. The weight can vary, but a common approach is to use a ratio of B = 1, P = 4, and W = 1. The expected task duration is calculated as follows: (B+4 P+W)/6 Slide 12

Estimating Task Completion Time and Cost For example, a project manager might estimate that a file-conversion task could be completed in as few as 20 days or could take as many as 34 days, but most likely will require 24 days. Using the formula, the expected task duration is 25 days, calculated as follows: (20+(4*24)+34)/6 = 25 Slide 13

Critical Path A critical path is a series of tasks which, if delayed, would affect the final completion date of the overall project. For Example: As you can see in Above Figure 3 -16, Task 5 cannot begin until Tasks 3 and 4 both are completed. In this case, Task 4 is the controlling factor, because Task 4 finishes on Day 65, which is 20 days later than Task 3, which is completed on Day 45 Tasks 1, 2, 4, and 5 represent the critical path. Slide 14

Transforming a Task List into a PERT/CPM Chart You construct a PERT/CPM chart from this task list in a two-step process: STEP 1: CREATE THE WORK BREAKDOWN STRUCTURE STEP 2: ENTER START AND FINISH TIMES FIGURE 3 -17 Example of a table listing 11 tasks, together with their descriptions, durations, and predecessor tasks Slide 15

CREATE THE WORK BREAKDOWN STRUCTURE Slide 16

STEP 2: ENTER START AND FINISH TIMES FIGURE 3 -19 To complete the PERT/CPM chart, you apply the guidelines explained in this section. For example, Task 1 has a one-day duration, so you enter the start and finish for Task 1 as Day 1. Then you enter Day 2 as the start for successor Tasks 2 and 3. Continuing from left to right, you add the duration for each task to its start time Slide to 17 determine its finish time.

there are three important rules you must keep in mind: • If a successor task has more than one predecessor task, use the latest finish time of the predecessor tasks to determine the start time for the successor task. • If a predecessor task has more than one successor task, use the predecessor task’s finish time to determine the start time for all successor tasks. • Continuing from left to right, add the task duration for each task to its start time to determine and enter its finish time. Again, be very careful not to add too many days. For example, if a task starts on Day 10 and has a duration of 5 days, then the finish would be Day 14 — not Day 15. Note: When you have entered all the start and finish times, you determine that the project will be completed on Day 155. Also, you note that Tasks 1, 2, 4, 6, 9, and 11 represent the critical path, as in figure Slide 18