Project Schedule Development Process

Project Schedule Development Process
Project Schedule Development Process

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?

Project Schedule is a list of activities that need to be performed in order to fulfill the project scope. This list is organised in a logical sequence, also called the schedule network logic. The list consists of activity duration, constraints, inter-dependencies among the various activities, activity lead and lag and the resources required to complete the schedule activity. Project schedule specifies the planned start and finish dates of each activity likely to be executed in a project, it also specifies the dates when important projects milestones have to be met. The project scope statement is a key input in developing a project schedule. The project schedule serves as a baseline against which the project progress can be tracked.

The Steps for Project Schedule Development Process:

Following paragraphs enumerate the steps involved in project schedule development process.

Step 1: Review all information relating to time management that serves as a basis of defining each activity.

Project deliverable assumptions and constraints documented in Project Scope Statement and the Project Schedule Management Plan are important documents that should be considered while developing the project schedule. Project Work Breakdown Structure, Organisational Policies relating to activity definition, lessons learnt from previous project, activity list of previous similar project are other documents that should be referred to while developing a project schedule.

Step 2: Support each element of the project scope, as defined in the WBS, by an activity or activities.

Identify the deliverable at the lowest level in the WBS called the work packages. Subdivide the work packages into smaller, more manageable components called schedule activities. The process of dividing the work packages in to more manageable components is called decomposition. Rolling wave is another tool that can be used in developing a project schedule. Rolling wave planning is form of progressive elaboration planning where the work to be performed in near term is planned in detail as compared to the work that are at higher level of WBS component. Therefore, schedule activities can exist at various level of detail in a project life cycle.

Step 3: Define activities uniquely; include a verb, at least one object, and any useful clarifying objectives.

While defining the activities include the scope of work description in quantifiable terms for each schedule activity so that the project team member can understand in sufficient detail what work is required to be performed.

Step 4: Define the activity list.

The activity list is comprehensive list including all schedule activities planned to be performed on a project. The activity list does not include any schedule activities that are not required as part of project scope. The schedule activities are discrete components of the project schedule, but are not components of WBS. The schedule activities have certain attributes like activity identifier, activity code, activity description, predecessor activity, successor activity, lead and lag, assumption and constraints, resources requirements, Schedule activity can also include other attributes like level of effort, person responsible, geographical location etc. 

Step 5: Determine and record the order in which the activities will be performed

The activity list generated as a result of step 1 to step 4 is an input to next stage of schedule development process. The logical relationship among various schedule activities need to be established and documented, also identify the leads and lags among various activities. Relationships among various schedule activities can be established by constructing the schedule network diagram.
Precedence Diagramming Method (PDM) is an important tool used to establish precedence relationships. PDM is also called Activity-on-Node (AON) and is used by most of the project management software.
The PDM method has four types of precedence relationships or dependencies:

(a) Finish-to-Start:

The initiation of successor activity depends on the completion of predecessor activity.

(b) Finish-to-Finish:

The completion of successor activity depends on the completion of predecessor activity.

(c) Start-to-Start:

The initiation of successor activity depends on the initiation of predecessor activity.

(d) Start-to-Finish:

The completion of successor activity depends on the completion of predecessor activity.
Arrow Diagramming Method (ADM) is another method to establish the logical relationships among schedule activities. This technique is also called Activity-on-Arrow (AOA) and is less prevalent than PDM/AON.
There are three types of dependencies that the project management team should impose on the schedule are 

(a) Mandatory Dependency:

Inherit to the nature of work being performed

(b) Discretionary Dependency:

Established based on knowledge of best practices in a particular application area or where a specific sequence is desired based on past experience on a successful project. This is also referred as preferred logic, preferential logic, or soft logic.

(c) External Dependency:

External dependencies are those that involve a relationship between project activities and non project activities.

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

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