Relationship between WBS and Gantt chart

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lopy
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Dear Experts,

I'm wondering what is the difference between WBS and Gantt chart. Can i say that Gantt chart is WBS with time and resources assigned? I read that i should not state work unit into WBS. Is it right? Why is it so?

How do you create a Gantt from WBS in practice? Use the structure and insert a work units?

Thank you in advance
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dhaughey
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Hi Lopy,

An excellent question and something that often confuses people.

A Work Breakdown Structure (WBS) is a hierarchical decomposition of a project into manageable chunks. It is graphical and shows all the project parts in an organised chart. Unlike a Gantt chart, it does not show the tasks organised in sequence over time. WBS is used at the start of a project to define the scope, estimate costs, allocate resources, manage risk and create schedules. A good WBS looks like an Organisation chart or Tree diagram, with all parts connected and no redundancy.

A Gantt chart is created from the Work Breakdown Structure and is a bar chart that tracks tasks across time. It shows the start and finish date of each task and their relationship to each other. A tracking Gantt chart can be used to show progress over time, using a percentage completed for each task and whether ahead or behind against today's date. A Gantt chart also shows the Critical Path; the longest duration path through the schedule. If a task on the Critical Path is delayed by one day, the entire project will be delayed by one day. Microsoft Project is the best known tool for creating Gantt charts.

To create a WBS you must first identify the main deliverables of your project. Once this is done, you start breaking down the deliverables into smaller chunks of work and creating branches. You continue breaking down your tasks until you reach a point where they are manageable. As a general rule of thumb, most people consider manageable as two weeks work.

To create a Gantt chart from your WBS, you will need to update the branches, so they become a task list. You may need to rearrange the branches, removing some tasks and adding others. Add the duration (usually in days) and a start date to each task. Link tasks together so they are in a logical order. Review your dependencies; what tasks are dependent on another being completed? Make sure you do not start a task with a dependency before the preceding task is finished. Finally, add resources to each task, being careful not to over use anyone.

Please note, the PRINCE2 method does not use the WBS but uses a Product Breakdown Structure (PBS). Similar in format to the WBS, a PBS documents the required outputs or products needed to deliver the project.

Does this help?

Duncan
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kwalford
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dhaughey wrote:Hi Lopy,

An excellent question and something that often confuses people.

A Work Breakdown Structure (WBS) is a hierarchical decomposition of a project into manageable chunks. It is graphical and shows all the project parts in an organised chart. Unlike a Gantt chart, it does not show the tasks organised in sequence over time. WBS is used at the start of a project to define the scope, estimate costs, allocate resources, manage risk and create schedules. A good WBS looks like an Organisation chart or Tree diagram, with all parts connected and no redundancy.

A Gantt chart is created from the Work Breakdown Structure and is a bar chart that tracks tasks across time. It shows the start and finish date of each task and their relationship to each other. A tracking Gantt chart can be used to show progress over time, using a percentage completed for each task and whether ahead or behind against today's date. A Gantt chart also shows the Critical Path; the longest duration path through the schedule. If a task on the Critical Path is delayed by one day, the entire project will be delayed by one day. Microsoft Project is the best known tool for creating Gantt charts.

To create a WBS you must first identify the main deliverables of your project. Once this is done, you start breaking down the deliverables into smaller chunks of work and creating branches. You continue breaking down your tasks until you reach a point where they are manageable. As a general rule of thumb, most people consider manageable as two weeks work.

To create a Gantt chart from your WBS, you will need to update the branches, so they become a task list. You may need to rearrange the branches, removing some tasks and adding others. Add the duration (usually in days) and a start date to each task. Link tasks together so they are in a logical order. Review your dependencies; what tasks are dependent on another being completed? Make sure you do not start a task with a dependency before the preceding task is finished. Finally, add resources to each task, being careful not to over use anyone.

Please note, the PRINCE2 method does not use the WBS but uses a Product Breakdown Structure (PBS). Similar in format to the WBS, a PBS documents the required outputs or products needed to deliver the project.

Does this help?

Duncan
Hi Duncan,

I have a question on this, do you use a Product Breakdown Structure (PBS) first and then create a WBS once the deliverables are known? Or, do you skip out the PBS and go straight into formulating the WBS? This has intrigued me before as it would appear some PM's don't use a PBS and just a WBS...

Many thanks,
Kit
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dhaughey
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Hi Kit,

Personally, I go straight to the WBS and skip the PBS. They both look similar; however, the PBS breaks down the outcomes of the project (your end goal) while the WBS breaks down the activities needed to achieve that end goal.

If creating both, I'd start with the PBS, which will give you your deliverables and then map that across to your WBS to give you the activities needed to realise the deliverables.

For me, deliverables and outcomes are specified in a BOSCARD, so it is important to cross reference them with the WBS to make sure there is no missing work.

In short, the PBS tells me about the product I'm delivering to the customer, and the WBS tells me how I'm going to do the work. That's how I see it.

Thanks,
Duncan
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kwalford
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dhaughey wrote:Hi Kit,

Personally, I go straight to the WBS and skip the PBS. They both look similar; however, the PBS breaks down the outcomes of the project (your end goal) while the WBS breaks down the activities needed to achieve that end goal.

If creating both, I'd start with the PBS, which will give you your deliverables and then map that across to your WBS to give you the activities needed to realise the deliverables.

For me, deliverables and outcomes are specified in a BOSCARD, so it is important to cross reference them with the WBS to make sure there is no missing work.

In short, the PBS tells me about the product I'm delivering to the customer, and the WBS tells me how I'm going to do the work. That's how I see it.

Thanks,
Duncan
Hi Duncan,

Thanks for the clarification. It is interesting to see what techniques/methods people use. Prince2 advocates the PBS but I don't see many people using it really in practice, well not that I have seen anyway.

Happy new year too.

Many thanks,
Kit
NickC
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This is a good post.

When I started using Prince2 I created PBS's / WBS's initially but I soon went back to using the Gantt format as a starting point as I felt like there was too much duplication by creating separate documents.

A possible disadvantage of not having separate documents could be that brainstorming / ideas sessions are less creative because the Gantt format is less visual than a tree / mind-map format. Also Gantt charts tend to encourage the team to start thinking about timing, dependencies and resources and less about breakdown structures.

My projects tend to follow similar formats and I can usually get away with not having specific PBS's / WBS's.
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dhaughey
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Hi Nick,

I don't think you're alone, plenty of project managers go straight to a Gantt chart for planning and manage without the WBS / PBS. The main issue I see with this is the risk of missing important activities needed to meet the end goal. The benefit of the WBS for me is the decomposition process, uninhibited by timelines, resources, dependencies etc. This encourages the team to concentrate on breaking down the activities needed to complete the project and not focussing on how they're going to do the work.

Duncan
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kwalford
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What type of WBS structure is your preferred model?

For example, Hierarchical Structure, Tree structure, Tabular table etc. The Tree Structure seems to be the most common.
Jacob Samuels
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To plan timing task Gantt chart tool is used. Time required for specific task can be shown by a horizontal bar. Digits at start of bar will show timing to start the task and end of bar shows when it should be completed. We can also determine which tasks are running parallel and which are running separately. Also we can find task dependancies.

WBS is representation of complex project in simple way. It includes major elements of project. In WBS we can enlist task name, estimate of time and responsible person.
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dhaughey
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I prefer a graphically expressed WBS. It's easier to work with and for people to understand over the tabular form. I'd like to note that all Work Breakdown Structures are hierarchical whether tabular, tree or any other structure.

For me, a good WBS is the basis of any well planned project. Get this right and you are well on your way to a success.

Duncan
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