In project management scheduling is the listing of activities and milestones for a project from start date to finish date. Moreover, this listing is based on logical and sequential manner. A project schedule can be at a very top level showing some main activities and milestones. This high-level project schedule is prepared for the top management understanding. While, detailed project schedule is prepared using work breakdown structure (WBS) document. This detailed project schedule is used to monitor and control the project at execution level. To know more about WBS you can go through my article on Work Breakdown Structure. In this article we will go through various project scheduling techniques used in project management.
First of all, let us understand different types of dependency relationships of tasks in a project management schedule.
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Tasks Dependencies in Project Management
There are below four types of task dependency relationships. In simple words, dependencies are the relationships of predecessor activities to the successor activities. These relationships tell us in a logical way, how different tasks we should take up on it.
Finish to Start – This is the most common dependency relationship. In these types of activities previous task or predecessor must finish before next task or successor can start. Example for this can be completion of civil foundation before equipment erection.
Start to Start – here predecessor task must start before the successor task can start. We can understand this by the example of equipment erection and piping work. It means to start piping work, first you should start equipment erection.
Finish to Finish – this is the type where predecessor activities must finish before successor activities finish. For this, example can be piping work must finish before instrumentation activities finish.
Start to Finish – in this dependency where predecessor task must start before successor task can finish. Example can like structure work must start before painting work finish. In project scheduling methods, this relationship is least common.
During preparing project schedule we need to understand above dependency relationships between various tasks clearly.
Now in next section, let us go through main project scheduling techniques which are commonly used.
Project Scheduling Techniques
As we know project schedule is the list of milestones and all the activities within a project from start to finish. Also, this schedule is based on the project work breakdown structure which provides duration and resource requirement for each project activity. Using project scheduling we can list down the activities in a logical and sequential manner to achieve best possible early finish date to complete project work. In other words, we can estimate the duration of complete project scope of work. Moreover, if you have a proper project schedule ready, then time management and adjustments with the scope of work of a project is easily possible. So, let us discuss commonly used project scheduling tools and techniques as below:
Critical Path Method (CPM)
Each project has a critical path, which is the total duration of start to finish interlinked activities. However, in a project schedule there can be many paths from start to finish date of a project. But, when we talk about Critical Path, it is the longest path among all the possible other paths to complete a project work. Also, a critical path has the least float available. Below are some definitions, which we use in project schedule:
Float – Is the amount of time duration up to that you may delay an activity from it’s early start without delaying the project finish date. Also, when a float is sharable among other activities it is known as Total Float.
Critical Activity – All the activities which lies in critical path, we call them critical activities.
It is very important to understand, you can not delay the activities of critical path, otherwise your project will not finish on time. Also, the critical path in a project is dynamic in nature and it is not fixed.
Example for CPM
Let us take a hypothetical example to understand the CPM technique. For this below is a network diagram which we can draw.
In above project network diagram, we can see there are three paths between start to finish date of the project. Which we can write as below:
1> Path -1: Start – A – C – F – Finish = 3 + 7 + 8 = 18 days
2> Path -2: Start – B – D – F – Finish = 5 + 1 + 8 = 14 days
3> Path -3: Start – B – E – G – Finish = 5 + 7 + 5 = 17 days
Therefore, in case of above project Path -1 is the critical path, since it has longest duration required for completion (which is 18 days). So, as a project manager you should focus on the activities of Path -1 very critically. You should understand completing this project before 18 days is not possible for given resources. Other two paths, Path -2 & Path -3 have slack or float of 4 days and 1 day respectively. It means if you delay Path -2 activity by <4 day it will not affect the total project completion duration. Similarly, for Path -3 you have 1 day slack time.
Also, you need to understand in a project, critical path is dynamic in nature. It means, if initially one path is critical, it is possible in later stage of project another path can be a critical path. Let us consider the above example, if because of some unforeseen reason in Path -2, activity ‘D’ duration changes from 1 day to 7 days, the total duration will become 20 days. So, now Path -2 is the longest and will be the critical path for this project.
Program Evaluation & Review Technique (PERT)
There are situations, when many uncertainties are present in your project, then critical path method technique is not so handy. In those circumstances, we can use PERT, which is also similar to CPM. However, this technique is based on three time estimates to determine the duration of an activity. These three-time estimates are Optimistic, Pessimistic and Most Likely. So, we can estimate the duration of an activity as below:
Estimated Duration = (Optimistic + 4*Most Likely + Pessimistic)/6
Main differences found between PERT and CPM techniques are, PERT is probabilistic whereas CPM is deterministic. In CPM, estimates of activity duration are based on historical data, while in PERT, estimates are uncertain (i.e., estimated based on above relationship). In PERT we talk of ranges of duration and the probability that activity duration will fall into that range. While, the CPM concentrates on Time/Cost trade off, high-cost low time required or vice versa.
Moreover, other techniques which we can find are Resource Constrained Project Scheduling Problem (RCPSP) Model, Search based techniques, Event Based Scheduler (EBS), etc.
Resource Planning and Allocating
In a project schedule when we assign a duration it depends on physical resources such as man, machine, material and money. Also, this time duration depends on quantities of each resource will be used to complete the project activities. As a project manager, you need to assess in advance and allocate the various resources to the activities coming in line as per the project schedule. This is very critical, to ensure smooth execution of the project.
Moreover, as a project manager you need to consider both qualitative and quantitative aspects of the human resource. So, during estimating project completion duration you need to be very realistic, otherwise there can be many unpleasant outcomes in future.
Therefore, resource management is very critical for the timely completion of your project. So, typically in resource management we cover below things:
- Resource allocation and it’s impact one completion time and project cost.
- Resource levelling and smoothing, to reduce the load and stress on resources, especially on the human resource.
For resource management commonly we use two techniques, which are Resource Histogram and S-Curves.
Resource Histogram – Using this technique, we can understand and get insight on the resource allocation status of the project. Moreover, we can know how resources are impacting the project progress. We can develop resource histogram, from quantity of resource allocation to various activities during the project. And, based on criticality of the activities appropriate decisions we can take to mobilise the resources from one activity to another.
S-Curve – We can prepare S-Curve for planned activity schedule and can compare it with actual S-Curve to access the project progress performance. S-Curve is the plot between cumulative total of a resource with respect to the project time line.
Gantt Chart
As a project manager we all need to prepare a Gantt Chart or a project activity bar chart for our project. In project management, Gantt chart is a tool which we use in scheduling techniques and shows a project plan. In this we see there are two parts, left side there are list of tasks or activities. While, other side includes timeline with schedule bars that shows work duration. In Gantt chart there can be lots of other information like, start and end dates, dependency relationships among activities, milestones, resources, baseline, actual start & finish dates, etc.
Below is the Gantt chart for above mentioned example. This I have prepared on Microsoft Project Scheduler; in this we can see project calendar has 5 days working week. However, we can change this, by selection & customizing different calendar.
We use Gantt charts for planning and scheduling in project management. Using it we can monitor and control the project progress. Apart from this you can take timely decision for resource requirements, so that tasks complete on scheduled date. Also, you can manage dependency relationships between activities very easily.
Conclusion
Finally, as a project manager we need various resources (man, machine, money, material) to carry out and complete our projects. Moreover, any organization has fixed resources and as a project manager you are responsible to allocate them after reviewing meticulously. So that, project work can be finished within budgeted time and cost.
So, to meet above objectives, we tried to understand various project scheduling tools & techniques in this article. Which includes CPM, PERT, Gantt Chart and Resource Planning. We should use project scheduling software to develop our project schedules, which are easy to use. I have used Microsoft Project during my work experience and found it very useful. Using this project scheduling software, we can easily monitor and control our project progress, resource requirement and overall project cost.
Thanks for reading.