Project Scheduling - Explained
What is Project Scheduling?
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Table of ContentsWhat Is Project Time Management?What Is Project Scheduling?PMBOK Process for Schedule ManagementWhat is Plan Schedule Management?What is Network Analysis?What is the Program Evaluation and Review Technique (PERT)? How to Identify Project Activities?How to Estimate an Activity Duration? How to Identify Activity Relationships?What is the Critical Path Method? What is the PRECEDENCE DIAGRAMMING METHOD (PDM) or ACTIVITY-ON-NODE (AON). What are Activity Predecessors?What are Leads and Lags?How to Draw a Network Diagram?How to Calculate the Earliest Start/Finish Times (forward pass)? How to Calculate the Latest Start/Finish Times (backward pass)? How to Calculate the Slack and Float Values? How to Determine the Critical Path? How to Calculate Drag? How to Use Graphic Representations in Sequencing? What is a Project Logic? What is a Milestones Schedule?What are the Types of Project Scheduling?How to Develop a Project Schedule?What is the Conceptual Project Schedule? What is a Master Project Schedule?
What Is Project Time Management?
Time Management is essentially the ability to organize and plan the time spent on activities. Project time management involves controlling the amount of time it takes to do the tasks required in the project.
The project team works to develop a project schedule to manage time and expectations during the project. This requires an analysis of the project scope, contract, and other information related to the project deliverables.
What Is Project Scheduling?
Project scheduling is the process of identifying tasks and assigning resources to the completion of the task.
A “Project Schedule” is a document that demonstrates all of the work required and time and time allowed to complete it. The schedule develops as the project moves from its early conceptual phase into the execution phase.
PMBOK Process for Schedule Management
Project time management in the PMBOK® Guide is made up of 7 processes. The project time management processes are:
• Plan schedule management
• Define activities
• Sequence activities
• Estimate activity resources
• Estimate activity durations
• Develop schedule
• Control schedule.
What is Plan Schedule Management?
The Schedule management plan is a part of the project management plan and can be formal or informal. It is basically a methodology used to create and manage the schedule.
The first step includes establishing all the policies, procedures, and documentation required for managing your project schedule. The objective is to create a plan for how to create and manage the project schedule.
In real-life practice, this is later incorporated into the project schedule. The schedule management plan is created as a part of Develop Management Plan process in Integration Management.
Creating a plan for managing the schedule involves thinking about the following:
- Individuals involved in the scheduling process
- The approach required to plan a schedule of the process
- Use of organizational processes and procedures
- Tools used for scheduling
- Method to manage and control the project to schedule baseline and manage any deviations
The project manager will identify the following:
- Scheduling software used
- Measurement guidelines i
- Estimated duration of each activity
- Resources or Efforts required for those activities.
This information is used to create a project baseline. This will be used to identify any variances in the schedule.
The project manager will also develop a Change Control Procedure. This is the process for managing changes to the schedule. The schedule management plan often controls the project reporting process.
What is Network Analysis?
Network analysis involves the following steps:
- Identifying project activities
- Estimating activity durations
- Identifying activity relationships
- Drawing the network diagram
What is the Program Evaluation and Review Technique (PERT)?
Network analysis/Project Evaluation and Review Technique (PERT) is a method to analyze the involved tasks in completing a given project, especially the time needed to complete each task, and to identify the minimum time needed to complete the total project.
The activities are presented as nodes and the duration of the activity is represented by lines between the nodes.
Of note, the PERT technique allows for flexibility in the period of time to complete a task.
How to Identify Project Activities?
Activities consume time and/or resources. The first stage in planning a project is to break down the project into a number of identifiable activities with a start and end. Performance objectives of time, cost and quality can be associated with each activity.
This identifies the specific tasks and activities that must be carried out to accomplish the project goals and produce the project deliverables. It is broken down by individual unit of work.
In scope management, the project team created the Work Breakdown Structure. The WBS resulted in Work packages that are used to define the activities.
The work packages are broken down into activities. Each activity is estimated, scheduled, monitored, and managed. This requires a an understanding of the scope of the objectives achieved by the activity and the availability or resources (the project team).
- Note: Much of this process involves estimation. As part of the process, he project manager’s use a technique called “rolling wave planning”. This approach defers planning specific details of the work only when he starts that phase of the project lifecycle.
The outcome of the activity definition process is the creation of:
- Activity list
- Activity Attributes
- Milestones - interim deliverables of the project schedule.
How to Estimate an Activity Duration?
Retrieve information concerning the duration of the tasks involved in the project. he can be collated from a number of sources, such as documentation, observation, interviewing etc.
Activity duration estimating is the process of determining how long each activity will take.
Specifically, for each activity in the activity list, consider its scope and resources, and estimate how long it will take to perform.
The common techniques for estimating activity duration include:
- Expert judgment - This come from the experience of the project team members.
- Analogous estimating - This is comparing similar activities from previous projects and how long they took.
- Parametric estimating - This generally involves using pricing formulas built into project management software. But, it can include the use of a any formula, spreadsheet, database, or computer program that comes up with an estimate.
- Three-point estimating - This process comes up with three cost estimates for each activity: realistic, optimistic, and pessimistic. The final estimate is the weighted average of the three.
- Reserve analysis - This means estimating the duration of an activity and then adding extra time to the schedule (called a contingency reserve or a buffer) to account for extra risk.
When determining duration, you want to look at the time require and the amount of effort required during that time - as the intensity of effort will affect the amount of time required.
Of note, you must take into account resource availability when calculating duration activity.
The duration is determined with the following formula:
TE = (O + 4M + P) ÷ 6
Expected time = (Optimistic time + 4*(most likely time) + pessimistic time)/6.
optimistic time (O): the minimum possible time required to accomplish a task, assuming everything proceeds better than is normally expected
pessimistic time (P): the maximum possible time required to accomplish a task, assuming everything goes wrong (but excluding major catastrophes).
most likely time (M): the best estimate of the time required to accomplish a task, assuming everything proceeds as normal.
expected time (TE): the best estimate of the time required to accomplish a task, accounting for the fact that things don’t always proceed as normal (the implication being that the expected time is the average time the task would require if the task were repeated on a number of occasions over an extended period of time).
How to Identify Activity Relationships?
A task waiting to begin is dependent on the former task. Tasks with independent relationship can occur simultaneously.
Critical path diagrams are used extensively to show the activities undertaken during a project and the dependencies between these activities.
What is the Critical Path Method?
The Critical path method creates a visual representation (network diagram) of the project, the tasks, the time period for each task. The focus is on the critical activities, but the non-critical activities are also identified.
First, the activities are identified, the duration is estimated, and the activities are sequenced to optimize efficiency.
In the network picture, the nodes represent activities. The time required for each activity is represented by lines or arcs in between nodes.
The length of time it takes to follow the path is the sum of all the durations of activities on that path. The path with the longest duration gives the project completion time.
Any change in duration in any activities on this path will cause the whole project duration to either become shorter or longer.
Activities not on the critical path will have a certain amount of slack time in which the activity can be delayed or the duration lengthened and not affect the overall project duration.
The amount of slack is a function of the difference between the path duration the activity is on and the critical path duration.
By definition all activities on the critical path have zero slack. It is important to note that there must be at least one critical path for each network and there may be several.
What is the PRECEDENCE DIAGRAMMING METHOD (PDM) or ACTIVITY-ON-NODE (AON).
The precedence diagram method (PDM) is a technique for graphically displaying the logic of the schedule by placing the activities in boxes with arrows between them to show the precedence-successor relationships.
With this activity, you will sequence the project times and durations based upon the finish and start times relevant to other activities.
The arrangements are as follows:
- Finish-to-Start (FS): The successor can start only after an activity finishes. This is the most commonly used relationship.
- Start-to-Start (SS): The successor can start only after an activity starts.
- Finish-to-Finish (FF): The successor can finish only after an activity finishes.
- Start-to-Finish (SF): The successor can finish only after an activity starts. This relationship is rarely used.
What are Activity Predecessors?
An activity that must occur first is a predecessor activity. The subsequent activity is a successor activity. The following are types of predecessor activities:
- External Predecessors - This is an activity that depends on things outside the project.
- Discretionary Predecessors - These are usually processes or procedures that are driven by best practices or performance standards. These are discretionary because they are a product or preference.
- Mandatory Predecessors - Mandatory predecessors are the kinds that have to exist just because of the nature of the work.
What are Leads and Lags?
A lead may be used to indicate that an activity can start before its predecessor activity is completed.
A lag is inserted waiting time between activities, such as needing to wait for completion of the application testing before the final roll-out of the application.
Sequence Activities process can also result in the identification of new risks.
How to Draw a Network Diagram?
The project network diagram, also known as a logic diagram, is a document that lays out the logical sequence of the activities needed to complete the project.
For the activity-on-node notation each activity task is represented by a node with the following format. A completed network will consist of a number of nodes connected lines, one for each task, between a start and end node.
How to Calculate the Earliest Start/Finish Times (forward pass)?
The early start date for an activity is the earliest date the activity can begin. The estimate considers durations and resource availability calendars.
To calculate early start dates, begin with the project start date and assign that date as the start date of activities that have no predecessor activities. Follow these steps to calculate the early start dates of subsequent activities, assuming finish-start relationships:
- Add the predecessor activity’s duration to its start date.
- Add the lag time or subtract the lead time.
- Refer to the resource calendar (or calendars) that applies to the people and equipment necessary for the activity, and add the number of off-days that the activity would span on those calendars.
- Assign the calculated date as the early start date of the successor activity.
Restated, you move left to right along the network, forward through time.
- Assume the start (i.e. first) task begins at time = 0.
- Calculate the earliest finish time where: Earliest Finish = Earliest Start + Duration
- Calculate the earliest start time of the next task where:-Earliest Start = Earliest Finish of task immediately before: If there is more than one task immediately before take the task with the latest finish time to calculate the earliest start time for the current task.
- Repeat steps 2 and 3 for all tasks
How to Calculate the Latest Start/Finish Times (backward pass)?
The lat start dates are the latest date each activity could begin and still meet the project completion date.
To do this, work through the network diagram from right to left beginning with the mandated completion date from the project plan, as follows:
- Subtract the predecessor activity’s duration from its late finish date
- Subtract the lag time or add the lead time to the late finish date.
- Refer to the resource calendar (or calendars) that applies to the people and equipment necessary for the activity, and subtract the number of off days that the activity would span on those calendars.
- Assign the calculated date as the late start date of the predecessor activity.
The difference between the early start date and the late start date for activities on the critical path is usually the same as the total float, unless the activities are affected by the resource calendars differently in the forward and backward pass.
Restated, you move right to left along the network, backward through time.
- Assume the end (i.e. last) task end time is the earliest finish time (unless the project end time is given).
- Calculate the latest start time where:- Latest Start = Latest Finish – Duration
- Calculate the latest finish time of the previous task where: Latest Finish = Latest Start of task immediately after. If there is more than one task immediately after take the task with the earliest start time to calculate the latest finish time for the current task.
- Repeat steps 2 and 3 for all tasks
How to Calculate the Slack and Float Values?
Float, sometimes called slack, is the amount of time an activity, network path, or project can be delayed from the early start without changing the completion date of the project.
The slack or float value is the difference between the earliest start and latest start (or earliest finish and latest finish) times for each task. To calculate the slack time
- Slack = Latest Start – Earliest Start OR Slack = Latest Finish – Earliest Finish
- Repeat step 1 for all tasks.
Total float is the difference between the finish date of the last activity on the critical path and the project completion date.
Any delay in an activity on the critical path would reduce the amount of total float available on the project.
Positive float is when you finish ahead of the finish date of the last activity. A negative float is when the calculated completion date of the last activity is later than the targeted completion date.
Free float are activities that are not on the critical path but have a difference between their early start date and their late start date, those activities that can be delayed without affecting the project completion date.
How to Determine the Critical Path?
Identifying the Critical Path: Any tasks with a slack time of 0 must obviously be undertaken on schedule at the earliest start time. The critical path is the pathway connecting all the nodes with a zero slack time. There must be at least one critical path through the network, but there can be more than one. The significance of the critical path is that if any node on the path finishes later than the earliest finish time, the overall network time will increase the same amount, putting the project behind schedule. Thus any planning and control activities should focus on ensuring tasks on the critical path remain within schedule.
How to Calculate Drag?
The drag of a critical path activity can be computed using the following formula:
- If a critical path activity has nothing in parallel, its drag is equal to its duration.
- If a critical path activity has another activity in parallel, its drag is equal to whichever is less: its duration or the total float of the parallel activity with the least total float.
How to Use Graphic Representations in Sequencing?
The relationship between activities should be presented in a graphic representation. Some of the approaches include:
Gantt chart - The Gantt chart, also called a bar chart, is a time-scaled graphic that represents each activity with a bar that reflects the duration, start, and finish time.
To draw a Gantt Chart manually undertake the following steps:
- Draw a grid with the tasks along the vertical axis and the time-scale (up to the project duration) along the horizontal axis.
- Draw a horizontal bar across from the task identifier along the left of the chart starting at the earliest start time and ending at the earliest finish time.
- Indicate the slack amount drawing a line from the earliest finish time to the latest finish time.
What is a Project Logic?
The project logic is an activity sequence or order of the activities that will be completed. Developing the project logic requires identifying the characteristics and identifiers of an activity are its attributes.
To begin, the project manager will determine the starting and ending point for each activity with relationship to other activities. That is, one activity (or multiple activities) may have to begin or completely finish before another can begin. Others may take place concurrently.
As such, the project logic identifies activities that must come first (predecessors) before other activities (successors). The relationship is known as “dependency”
Note: This predecessor-successor relationship relationship is often referred to as the “father-son” relationship.
What is a Milestones Schedule?
Milestones are significant events in your project. The project manager must create a schedule or milestones that identifies any constraints to reaching these milestones.
Note: Milestones are generally depicted by diamonds on the network diagram. It will be connected with a vertical line on a time-scaled graph to show the relationship of various schedule paths to the milestone.
The project schedule generally includes a milestone schedule. The milestone schedule establishes key dates throughout the life of a project. These milestones must be met for the project to finish on time.
What are the Types of Project Scheduling?
There are many different methods of scheduling. Generally, a method of project scheduling accomplishes the project objectives. The output of the scheduling process may vary with each method.
How to Develop a Project Schedule?
The next phase is developing the project schedule using the information assembled.
Depending upon the project phase, you will create one of the following schedules.
What is the Conceptual Project Schedule?
A conceptual or initial project schedule identifies important dates and activities. While it lacks details, it is generally used to allow the project sponsor or senior management to make decisions about the project scope. The scope document (containing the objectives, activities, and expectations) is used to create the project schedule.
What is a Master Project Schedule?
The master project schedule combines all of the work breakdown structure, project logic, and estimation of time to identify important dates (starting date, completion date, milestones) and activities.
Further, the major activities are broken into smaller activities with resources assigned to each.
The master schedule becomes a part of the employment contract. Further, portions of the master schedule may be provided to external parties (such as vendors) as part of the procurement and contracting process.