Practical steps in managing project schedules – II
Steps to developing a project schedule
- Step 1: Create a work breakdown structure
- Step 2: Estimate durations
- Step 3: Determine resources
- Step 4: Identify predecessors
- Step 5: Determine milestones
- Step 6: Identify dependencies
Step 1: Create a Work breakdown structure (WBS)
Definition - WBS A Work Breakdown Structure (WBS) is used for estimating the project scope by breaking it down into easily manageable components, or bites. WBS is the hierarchical list of project’s phases, tasks and milestones.
A WBS is very useful in planning a project and makes a complex project more manageable. The WBS is designed to help break down a project into manageable chunks that can be effectively estimated, managed and supervised.
A WBS also provides the basis for detailed duration and cost estimating. It gives accuracy in estimating a project by calculating how much time and effort is required to accomplish a task or activity, thereby aggregating to estimate effort required to complete a superior component in the hierarchy.
Following estimation techniques are commonly used in estimating a project scope:-
Top-down estimating: This technique is very useful in estimating the project when only high level requirements are known in a project and it is then decomposed progressively into smaller activities and work-packets. For example, activity excavation is broken top-down into activities ‘Pouring concrete’ and ‘Cure and strips formation’.
Bottom-up estimating: This technique is used when requirements are known at a discrete level where the smaller work pieces are then aggregated to estimate the entire project. This is usually used when the information is only known in smaller pieces. For example, lower level activities as building ‘Walls’, ‘Flooring’, ‘Roofing’, ‘Doors & windows’ may be individually estimated to arrive at duration required to complete ‘External Construction’.
WBS for a House Construction Project
The project is broken down into activities which is further decomposed into sub tasks or sub activities. The tasks done to complete the project are called activities. An activity is the lowest level subset in the project phase that is executed to accomplish a component of the project. Following is a WBS example for the construction of a House:
Define broader activities in the project
Begin by listing the high level activities (called summary tasks) required to do the project. Start mapping the lower level pieces or activities in hierarchy to the summary tasks. The high level activities (summary tasks) to construct a house are:
- External Construction
- Internal Construction
Define detail activities The project is broken down into lower level activities, subtasks and work packages till we arrive at a sufficient level of detail that supports the project plan.
Step 2: Estimate task duration
Once list of activities are identified, estimate the task duration for all activities as to how much effort by duration is required to perform each activity. To estimate the task duration, make sure the activity is detailed enough to estimate how much effort each activity or sub-activity will require to complete.
For example, to calculate how much time is required to complete the ‘Excavation’ for constructing the house, you may need to know what is involved in doing excavation and how much time is required to complete each activity in excavation. List the set of activities required to do excavation on the site and estimate the duration of each activity.
Step 3: Determine the Resources requirements
Determine the personnel and non-personnel resources required to perform all activities. For example, the excavation work may require following resources: Project Manager – Work duration 16 hours Site Grading Contractor – Work duration 80 hours
- Create Resource Table of all resources who will work on the project
- Assign or Allocate resources to activities
Step 4: Identify the dependencies between tasks
After identifying all the activities and timeline necessary to complete the project, we identify and define the immediate predecessors of all activities. This will determine the sequence in which the activities may be performed. For example, excavation work will be carried out before the steel erection can be done. Hence, predecessor to ‘1.2 Steel erection’ activity will be ‘1.1 Excavation’.
Step 5: Identify Dependencies
In a project, a dependency is a link between tasks or activities or elements. There are four kinds of dependencies:-
Finish to start (FS): A FS B = B can't start before A is finished or B will start only after A is finished. For example, concrete must cure before it can be used. Therefore, the builder pours the concrete, waits four days and then builds the walls on the concrete.
Finish to finish (FF): A FF B = B can't finish before A is finished, i.e., B will finish only after A is finished. For example, Foundations excavation cannot be completed unless elevator pit excavation is complete.
Start to start (SS): A SS B = B can't start before A starts, i.e., B can start only if A has started. For example, Curing cannot be started unless pouring for foundation has started.Start to finish (SF): A SF B = B can't finish before A starts, i.e., B can finish only after A has started. For example, Pouring & curing is a parallel activity and Pouring can finish only after curing has started.
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During the project planning phase, the project is estimated to list out the set of activities, tasks and resources required to complete the project. The project schedule is detailed enough to show each task to be performed, the resource allocated to perform the task, the start and end date of each task and the duration in which the task will be performed. During the lifecycle of a project, the project progress is monitored by the project schedule.
Step 6: Determine Milestones
The project is broken down into discrete chunks and the related tasks are grouped together as a phase or component. This phase or component of the project is assigned a measurable milestone as the target date or time to finish it. For example, based on the estimation of whole project, it is broken into phases with milestones as below:
|Phase||Duration||Target finish date|
|Foundation||45 days||15th Jan 2014|
|External Construction||180 days||18th July 2014|
|Internal Construction||60 days||5th Oct 2014|
Milestones are significant events that are either reached or imposed upon the project on completion of a phase. A milestone signifies the completion of a major phase in the project.
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