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Project Scheduling: Gantt/Pert Charts

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Presentation on theme: "Project Scheduling: Gantt/Pert Charts"— Presentation transcript:

1 Project Scheduling: Gantt/Pert Charts

2 What is a Project? A project is a (temporary) sequence of unique, complex, and connected activities that have one goal or purpose and that must be completed by a specific time within budget, and according to specification.

3 What is a Project? A project is a (temporary) sequence of unique, complex, and connected activities that have one goal or purpose and that must be completed by a specific time within budget, and according to specification.

4 Scheduling A schedule is the conversion of a project action plan into an operating timetable It serves as the basis for monitoring and controlling project activity work changes daily, so this is essential With the plan and budget, it is the major tool for the management of projects most scheduling is at the WBS level (tasks), not the work package level only the most critical work packages may be shown on schedule

5 Scheduling In a project environment, the scheduling function is more important than it would be in an ongoing operation Projects lack the continuity of day-to-day operations and often present much more complex problems of coordination

6 Scheduling The basic approach of all scheduling techniques is to form a network of activity and event relationships This network graphically portrays the relations between a project’s tasks Tasks that must precede or follow other tasks are then clearly identified, in time as well as function

7 Network Scheduling Advantages
Networks are a powerful tool for planning and controlling a project and have the following benefits: consistent framework for planning, scheduling, monitoring, and controlling the project illustrates the interdependence of all tasks, work packages, and work elements denotes the times when specific individuals must be available for work on a given task

8 Network Scheduling Advantages
aids in ensuring that the proper communications take place between departments and functions determines an expected project completion date identifies so-called critical activities that, if delayed, will delay the project completion time identifies activities with slack that can be delayed for specific periods without penalty

9 Network Scheduling Advantages
determines the dates on which tasks may (or must) be started if the project is to stay on schedule illustrates which tasks must be coordinated to avoid resource timing conflicts illustrates which tasks may (or must) run in parallel to achieve the predetermined project completion date relieves some interpersonal conflict by clearly showing task dependencies

10 Network Scheduling Techniques
PERT was developed in 1958 for the Polaris missile/submarine project The Critical Path Method (CPM) was developed by DuPont during the same time period Initially, CPM and PERT were two different approaches CPM used deterministic time estimates and allowed project crunching PERT used probabilistic time estimates Microsoft Project (and others) have blended CPM and PERT into one approach

11 Terminology Activity - A specific task or set of tasks that are required by the project, use up resources, and take time to complete Event - The result of completing one or more activities. An identifiable end state occurring at a particular time. Events use no resources. Network - The combination of all activities and events that define a project Drawn left-to-right Connections represent predecessors

12 Terminology Continued
Path - A series of connected activities Critical - An activity, event, or path which, if delayed, will delay the completion of the project Critical Path - The path through the project where, if any activity is delayed, the project is delayed There is always a critical path There can be more than one critical path

13 Terminology Continued
Sequential Activities - One activity must be completed before the next one can begin Parallel Activities - The activities can take place at the same time Immediate Predecessor – an activity that must be completed before a particular activity can begin An activity can be in any of these conditions: It may have a successor(s) but no predecessor(s) - starts a network It may have a predecessor(s) but no successor(s) - ends a network It may have both predecessor(s) and successor(s) - in the middle of a network

14 Terminology Continued
Activity on Arrow (AOA) - Arrows represent activities while nodes stand for events Activity on Node (AON) - Nodes stand for events and arrows show precedence

15 AON and AOA Format

16 Constructing an AON Diagram
Begin with the START activity Add activities without predecessors There will always be one There may be more than one 3. Add activities that have existing activities as predecessors 4. Repeat step 3 until no more activities

17 Gantt Charts Developed by Henry L. Gantt in 1917
Shows planned and actual progress Easy-to-read method to show current status

18 Gantt Charts: Advantages and Disadvantages
Easily understood Provide a picture of the current state of a project Difficult to follow with complex projects

19 Simple Schedule – Gantt Chart
© 2006 John Wiley and Sons, Inc.

20 Class Individual Exercise

21 Class Individual Exercise - 2.
Create a new Project Create the 12 Tasks from the previous slide enter their names and durations enter the task dependencies Now enter resources as follows: Jason Jeff, Emily Emily Jeff Ariel Pat Marsha Marc Save your work!

22 The Work Breakdown Structure
The Work Breakdown Structure (WBS) can take a variety of forms that serve a variety of purposes The total program can be described as a summation of subdivided elements. Planning can be performed. Costs and budgets can be established. Time, cost, and performance can be tracked. Schedules and status-reporting procedures can be established. (=> Gantt chart) Responsibility for each element can be assigned.


24 The Work Breakdown Structure - 2
The WBS often appears as an outline with Level 1 tasks on the left and successive levels appropriately indented The WBS may picture a project subdivided into hierarchical units of tasks, subtasks, work packages, etc.

25 Most common type: Six-Level Indented Structure
The Work Breakdown Structure - 3 LEVEL DESCRIPTION 1 Total Program Usually specified by the client and managed the project manager. 2 Project(s) 3 Task(s) 4 Subtask(s) Usually specified by the functional manager(s). 5 Work Package(s) 6 Level of Effort Most common type: Six-Level Indented Structure

26 Gozinto Chart for a Toy Bus

27 A WBS with more Breadth

28 The Work Breakdown Structure - 4
Summary: The WBS is an important document and can be tailored for use in a number of different ways It may illustrate how each piece contributes to the project in terms of performance, responsibility, schedule, and budget It may list the vendors or subcontractors associated with specific tasks It may serve as the basis for cost or schedule estimates It may be used to document that all parties have signed off on their various commitments to the project

29 The Work Breakdown Structure
Steps for designing and using the WBS: Using the action plan, list the task breakdown in successively finer levels of detail. Continue until all meaningful tasks or work packages have been identified. For each such work package, identify the data relevant to the WBS: personnel and organizations responsible for each task. All work package information should be reviewed with the individuals or organizations who have responsibility for doing or supporting the work to verify the accuracy of the WBS

30 WBS Linear Responsibility Chart

31 Simplified Linear Responsibility Chart

32 In-class Group Exercise
Create a WBS for your project

33 The AON Network

34 Critical Path and Time Notation: [Task name, expected time, variance]

35 Critical Path Calculation
To find the critical path: start with set of children of the Start node for each node: use the earliest start time (the greatest “earliest finish time of all this node’s predecessors), add in the duration to calculate the earliest finish time repeat step 2 for the children of each node in the set

36 Slack Calculation To find the slack:
start with End node and note its LS time for each predecessor node: set the LF time to the lowest LS time of the successor(s) and subtract the duration to get the EF time repeat step 2 for the children of each node in the set

37 Critical Path, Time, and Slack

38 Slack Values

39 Resulting Gantt Chart

40 Resulting AON Network

41 Calculating Activity Times
Notes: a is the optimistic estimate b is the pessimistic estimate m is an estimate of the mode TE is a calculation of the mean σ2 is the variance; a representation of the uncertainty σ is the standard deviation

42 The Results

43 Uncertainty of Project Completion Time
Assume activities are statistically independent is this reasonable? The variance of a set of activities is the sum of the individual variances We are most interested in variances along the critical path!

44 Fun With Statistics! What is the probability of completing a project on time, given a measure of variance and a critical path? We can answer that by calculating Z (# of standard deviations) as follows: Z = (D - ) / where D = desired project completion time = critical time of the project = variance of the critical path

45 Example Continued If we want to complete the project in 50 days then D = 50, μ = 43, = 33

46 Example - 2. The likelihood of completing the project in 50 days is 88.88% (see Table next slide) If we want 95% certainty of on-time completion: D = μ + σ * Z = * = days For 99% certainty D = * = days


48 Implications As D => μ, Z => 0
When Z = 0, probability of on-time completion is 50% Implication? If you want a high probability of being on time, you need some slack in the schedule! What about non-critical paths? Any path that has low slack and significant variance is a potential trouble spot.

49 Implications - 2. This is a great tool for you as a manager!
Your boss will want estimates. What is your basis for making them? Guesses?

50 In Class Group Exercise
Look at the WBS that you created for your project. From this, create a Gantt chart for your project. Determine the durations and dependencies for each of your project tasks. You only need to do “expected” duration for now.

51 In-class Group Exercise - 2
Calculate the total duration for your group project (and, hence, your critical path). Now, create a spreadsheet. For each project task, list: its optimistic, pessimistic, and expected durations you will have to do some educated guessing at this stage; that is normal

52 In-class Group Exercise - 3
Calculate TE, , and for each task Save this in your spreadsheet. Note for the critical path

53 In-class Group Exercise - 4.
Determine D for your project. Calculate Z. What is your probability of completing at time D? Submit your Gantt chart, your spreadsheet and an explanation of the WBS and the assumptions behind your estimates before next class.

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