WBS – a short rant

Well, not a rant really; more a lament.

It is actually a lament about how the fact that language is used differently across the two sides of the Atlantic can cause misunderstandings and, well…  rants.


I have been mystified for a while, about why some bloggers have commented – sometimes vehemently – on the need for Work Breakdown Structures to show deliverables, when it seems obvious to me that a WBS is a Work Breakdown Structure and, as I was taught, contains the Work or activities of the project.  It is a PBS or Product Breakdown Structure that contains the Products or Deliverables.

Shift Happens!

As I was researching for my forthcoming book on Project Risk Management, “Shift Happens!” I checked out the PMI’s PMBOK Guide (Fourth Edition).  This defines the WBS as a “deliverable-oriented hierarchical decomposition of the work…”

So what then is a PBS?  PMBOK does not define it, and so I see what has happened.  In the UK, we define (in “Managing Successful Projects with PRINCE2” Fourth Impression) a PBS as “A hierarchy of all the products …”

The “so what?”
Two nations divided by a common language

So we are all right.  A WBS focuses on the activities here in the UK and on the deliverables in the US.  Who knows about elsewhere?


11 thoughts on “WBS – a short rant

  1. Josh Nankivel

    I’ve run into this as well Mike, mostly with my WBS training course. From what I have discovered about the PBS and WBS on your side of the pond, it seems to me that this mapping comes about:

    West of Atlantic East of Atlantic
    WBS = PBS
    BOE = WBS + estimates

    My definition of the WBS is just about the same as your definition of the PBS. My Basis of Estimates (BOE) is where my teams and I decompose deliverables into work and document our estimates.


    1. Mike Clayton Post author


      Thank you. I too use a WBS + estimates as the basis for estimating costs, by mapping cost estimates to each activity on my WBS. This creates a Cost Breakdown Structure and is, to my mind, the best way to build a project budget. That way, the PM can track actual spend against budget as each activity is completed. It isn’t as sophisticated as full Earned Value Analysis (see my last blog) but its simplicity will make it appealing to many.

      I am also fond of a hybrid WBS/PBS tool that shows the tasks on a WBS, with the products that flow from the lowest level tasks linked to them, allowing a simple indexing of all deliverables with clear linkahge to the activity that finalises the product. A bit of a bodge-tool I know, but useful at times.

      Best regards


      1. Josh Nankivel

        Thanks Mike. I think it’s just a different way of doing the same thing. I like the BOE concept because it forces me and my teams to document our assumptions and rationale for coming to a particular estimate, which is helpful for change management because we can easily revisit our estimates when our assumptions turn out to be wrong.

        That said, I’m fond of using mind mapping to decompose work from the lowest level of our WBS (product-based) into tasks (your WBS content). Then I transfer this to the BOE so it’s more of a temporary tool for generating a decomposition of what is going to be delivered.



  2. John

    Hey Mike: On this side of the pond, the WBS originated in the Defense Department, going back into the ’60s at least, as now given in MIL HDBK 881A, now in its upteenth upgrade and reprinting. PMI is a very late comer to the ‘definition’ game. DoD has always defined the WBS in terms of the product of the work, not the work itself. The 881A definition is: “A product-oriented family tree composed of hardware, software, services, data, and facilities. The family tree results from systems engineering efforts during the acquisition of a defense materiel item. ” You can read all about it at http://www.acq.osd.mil/pm/currentpolicy/wbs/MIL_HDBK-881A/MILHDBK881A/WebHelp3/MILHDBK881A.htm

  3. Glen B Alleman

    Thanks John, you beat me to it. Mike on the government and large ERP programs we work, we live by the WBS. Yes it says works, but if you download 881 and read.

    “The Program WBS provides a framework for specifying program objectives. It defines the program in terms of hierarchically related, product-oriented elements…” is a starting point.”

    “The goal is to develop a WBS that defines the logical relationship among all program elements to a specific level (typically Level 3) of indenture that does not constrain the contractor’s ability to define or manage the program and resources. ”

    “Further, the WBS serves as a coordinating medium. Through the Program WBS and the Contract WBS, work progress is documented as resources are allocated and expended. Performance, cost, schedule, and technical data are routinely generated for reporting purposes.”

    I’d conjecture, that without a WBS you’ll have a hard time stating what “DONE” looks like.

    1. Mike Clayton Post author

      Thank you. Whether your WBS consists of products or tasks, I absolutely agree that it defines done. I use the WBS as the formal tool for defining scope. So it doesn’t only define done, it defines what has been commissioned (and therefore what has not).

      1. Glen B Alleman


        The WBS does not include tasks in its formal definition. Many IT PMs are confused about the WBS
        Please down load

        The PMI WBS Practice guide is OK, but the 881A is free.

        The WBS is a Product Breakdown and the Processes that are used to construction those products. The processes are things like “tooling,” “assembly.”

        The work effort is defined in the Integrated Master Schedule, traceable to the WBS. The Organizational Breakdown Structure (OBS) defines the resources (people and services – subcontractors e.g.) who produce those products. The intersection of the OBS and WBS is where the work is controlled.

  4. John

    Mike: re PERT, yes, I am familiar with the Polaris program and the invention, if that is the word, of PERT as a risk reduction tool by the Navy’s system engineering contractor, Booze-Allen-Hamilton. Mil 881 may be that old, or there was a predecessor document. To find the real headwaters, you probably have to go to the Air Force PMO that was formed in the mid-50’s to invent the ICBM and the IRBM. TRW, then Ramo-Woolsey [Thompson had not yet lent his “T” to the company], was the AF’s system engineer and system integrator. Air Force credits this SPO [as it was called] and TRW for “inventing” system engineering for the Air Force; WBS is a tool of system engineering as much, or more so, than project management.

    1. Mike Clayton Post author

      Someone should write a book (they probably have …) on the impact of warfare on human development. You can trace it through art, literature, science, commerce, music, psychology, …

  5. Pingback: Your project plan needs detail | Project Management Training with Ron Rosenhead

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