Accurate estimation using work break down structure (WBS)

Question

I am new to estimation techniques. I am trying to compare different techniques; mainly Use Case Point (UCP), Function Point (FP) and Work Breakdown Structure (WBS). In WBS context can I say:

1. WBS approach is dependent of the technology being used (e.g. Java/.Net will have different estimation figure).
2. It helps to roll up the effort across various tasks.
3. This technique would be more reliable if there are complexity guidelines that help to arrive at the individual task effort.
4. Unlike UCP/FP WBS does not help me to arrive the application size.

Are these understandings correct?

Answer 1

I would like to say that it is better to replace Work Breakdown Structure with a Requirements Breakdown Structure. So you can copy and past your Requirements Breakdown Structure from Requirements Specification to MS Project without any transformations ;) Using Breakdown Structure you are going to use so called expert estimation (e.g. PERT). The idea is that for expert it is easier to estimate a little work rather then big one.

1. As any expert effort estimation.
2. Yes.
3. Estimation is done by experts (at least two) without any guidelines. They are experts on that technology :)
4. Yes.

For projects less then 1000 FP it is usually not important whether to use FPA or Expert estimation. But with FP it is easier to maintain your estimation due to unavoidable requirements changes. Bigger than 10000 FP - definitely use FPA. If you do not have experts in certain technology you cannot use expert estimation. If you do not have knowledge base for similar projects and unaware of velocity of your potential project team (hours per FP) you cannot convert size to effort before project start.

Answer 2

Which technique to use depends on what kind of requirements/specification you have. If you have rough specification, WBS will help. If you already have the use cases written, UCP will do.

1. The WBS itself does not depend on the technology. Decomposition can be the same both for estimating for Java and .NET, the values will differ based on developers' skill and experience.

2. Yes, the effort will be estimated for each sub-task.

3. WBS recommends a least 3 levels of decomposition. From my practice, it's better not to have tasks for more than 20 hours.

4. Not sure if I understood you correctly, but by summing up all the sub-tasks you will receive the estimation for the whole project.