Managing time ‘Time is nature’s way of stopping everything happening at once’ Hughes & Cotterell 2002 Production Process

Lecture content Recap on last week Scheduling What is Critical Path Analysis? – Why use CPA? – Problems associated with CPA – How to perform CPA

Recap on last week Stakeholders Identifying the goals of the project Defining tasks – Activity based approach – Product based approach – Hybrid approach

Scheduling Scheduling is the process of assigning tasks to a set of resources. It is an important concept in many areas such as computing and production processes. In mathematical terms, a scheduling problem is often solved as an optimisation problem, with the objective of maximising a measure of schedule quality.

Scheduling Forward scheduling planning the tasks from the start date. Reverse scheduling planning the tasks from the due date.

CPA & PERT Critical Path Analysis and PERT are powerful tools that help you to schedule and manage complex projects. Developed in the 1950s to control large defense projects. Have been used routinely since then.

Why use CPA? Shows the sequence of activities Shows dependencies Aids scheduling resources & financial planning Used as a basis of control Diagrammatic therefore easier to read

What is Critical Path Analysis? 1. Using intertask dependencies, determine every possible path through the project. 2. For each path, sum the durations of all tasks in the path. 3. The path with the longest total duration is the critical path.

Problems associated with CPA Pay too much attention to critical path Experience needed to gauge durations Difficulties in separating tasks Only deals with numbers Doesn’t guarantee good project management, nothing does!!!

Events v. activities Event = a point in time – has no duration – e.g the start or end of an activity Activity = a task or an action with a recognisable start and finish and a duration Prepare breakfast Eat breakfast activities events

Start & Finish times Activity = a task or action with a recognisable start/finish time e.g. ‘write report software’ Earliest start (ES) Earliest finish (EF) = ES + duration Latest finish (LF) = latest task can be completed without affecting project end Latest start = LF – duration Earliest start Latest finish Earliest finish Latest start activity

Example Earliest start = 5 days Latest finish = day 30 Duration = 10 days Float = LF-ES-Duration Earliest finish =? Latest start = ? Float = ? The total float of an activity is the amount of time by which the task may be extended or delayed without delaying completion of the project.

Notation Activity description Activity labelduration ES LS EF LF Activity span Float

Earliest start time/date Earliest start date for the current activity = earliest finish date for the previous When there is more than one previous activity, take the latest earliest finish Note ‘day 7’ = end of work on day 7

Example EF = day 7 EF = day10 ES = day 10

What is the ES for G? A B C D F E G ES = day 0 Duration 5 Duration 6 Duration 10 Duration 9 Duration 8 Duration 3 Duration 4

Complete the table

Latest start date Start from the last activity Latest finish (LF) for last activity = earliest finish (EF) work backwards Latest finish for current activity = Latest start for the following More than one following activity - take the earliest LS Latest start (LS) = LF for activity - duration

LS for all activities? A B C D F E G ES = day 0 Duration 5 Duration 6 Duration 10 Duration 9 Duration 8 Duration 3 Duration 4

Complete the table

Now add the float!

Answer

Find the Critical path Note the path through network with zero floats Critical path: any delay in an activity on this path will delay whole project Can there be more than one critical path? Can there be no critical path? Sub-critical paths

Estimating task duration 1. minimum amount of time it would take to perform the task = optimistic duration (OD). 2. maximum amount of time = pessimistic duration (PD). 3. expected duration (ED) 4. Calculate the most likely duration (D) as follows: D = (1 x OD) + (4 x ED) + (1 x PD) 6

Something to think about… Can we truly say that by adding more human resource to a project it will reduce the time it takes to perform the task?

Further Reading PM_04.htm PM_04.htm of.htm inc.com/projex/PERT/cpa.htm inc.com/projex/PERT/cpa.htm eatures/criticalpath/default.asp eatures/criticalpath/default.asp