Project schedule development process is an iterative process and continues through out the project as work progresses. Project schedule is updated as the duration, resource estimates change on account of changes to project scope and budget. Anticipated risks may occur or disappear and this may also result is updating the project schedule. Before we start with the project schedule development process let us understand what is a project schedule.
What is a Project Schedule?
The Steps for Project Schedule Development Process:
Step 1: Review all information relating to time management that serves as a basis of defining each activity.
Step 2: Support each element of the project scope, as defined in the WBS, by an activity or activities.
Step 3: Define activities uniquely; include a verb, at least one object, and any useful clarifying objectives.
Step 4: Define the activity list.
Step 5: Determine and record the order in which the activities will be performed
(a) Mandatory Dependency:
(b) Discretionary Dependency:
(c) External Dependency:
Step 6: Develop initial activity sequence independent of resource availability
Any project requires men, material, and machines to complete the schedule. These resources are not available for an indefinite period of time. Availability of resource is scarce and needs to be planned in order to achieve the deliverable. Resource availability affects the planned schedule and therefore should be taken into consideration while developing a schedule.
Step 7: Apply discretionary dependencies to address resource availability
In order to develop a realistic schedule consider the resource availability for each and every scheduled activity. A resource calendar is an important input to this step. Identify the working days and non working days for the project, establish the availability of resources in terms of skills, knowledge, geographical location, duration of availability of resources to the specific project.
Step 8: In order to determine duration of each activity consider availability and productivity of each resource
The information required is schedule activity scope of work, required resource types, estimated resource quantities and resource calendar with resource availability.
(a) Estimate the amount of work effort required to complete the schedule activity
(b) Estimate the amount of resources required to complete the schedule activity
(c) Determine the no of work periods required to complete the schedule activity
Parametric estimating and three point estimates are the most important estimating tools and techniques. Parametric estimating technique considers multiplying the quantity of work to be performed by the productivity rate. Three point estimates are based on determining the three types of estimates viz Optimistic, Pessimistic and Most likely.
Step 9: Include two mandatory milestones: Project Start & Project Finish
Project start and Project finish dates are two most important milestone that should be incorporated in a schedule. No schedule can ever be made with out these two critical milestones.
Step 10: Link each activity in the schedule and calculate early and late start and finish dates
Early Start (ES) and Early Finish (EF) helps in deriving the activity float ie the freedom available to move the start dates of the activity without delaying the project finish date. Early start date of activity is the earliest time an activity can start similarly early finish date is the earliest time an activity can finish. Technique used to calculate the ES and EF of an activity is called forward pass.
Late Start (LS) it is the latest time an activity can start without delaying the project Late Finish (LF) is the latest time an activity can finish without delaying the project. The technique used to find LS and LF is called backward pass.Calculation of ES/EF, LS/LF is the core of the schedule network analysis and forms the basis of critical path analysis.
ES = EF of the immediate predecessor, for activities with more than one predecessor it is the latest of the earliest finish times of the preceding activities.
EF = ES plus the activity duration
LS = LF minus the activity duration
LF = LS of the activity that immediately follows, for activities with more than one activity that immediately follow, LF is the earliest of the LS of those activities.
Total Slack = LS – ES or LF – EF
Critical Paths have either a zero or negative total float/slack and it is the longest path in the schedule network between the start and finish dates
Total Float/Slack of an activity is the function of the performance of activities leading to it. It is shared by other activities.
Free Float/Slack is the amount of time that an activity’s earliest finish time can be delayed without delaying the earliest start time of any activities that immediately follows.
For a solved example of critical path method refer to my post
For difference between PERT & CPM refer to the following post