This question is one of the most frequently asked in project management courses. The simple explanation is the Work Breakdown Structure (WBS) represents all the parts and pieces of the project. What are all the parts necessary to complete the project? Sounds complex, right? Not necessarily.
When we begin a project, or even as we move through its life cycle, we want to try and identify everything that will go into getting to the finish line. What kind of resources will we need: people & “stuff”? Here’s the easiest method to use in identifying all this. Sit your initial team (or other interested parties) down and brainstorm what you think is needed. A good place to start is with the project charter. Unfortunately, the average charter is essentially nonexistent in a majority of small enterprises (and in some that are not small). For now, we’ll assume you actually have a charter and begin from that point forward.
Let’s assume you want to create a flower bed. (Yes, I know. Too easy, right?) Your significant other asked you to build one but didn’t clearly define what they wanted. So you go out to the garage and build a flower box for under the window. Wrong… Next step?
Snoogims actually wants to plant 10 rows each of beets and carrots 5 yards long and wants to be able to work the garden without having to bend down very far. Now you’re looking at a raised bed of a more specific size. What materials are you going to use? Wood, nails/screws, brackets, etc. How many and what size of each? How much and what kind of dirt will you need? Make a list. This is the beginning of your Work Breakdown Structure and it’s also what many people refer to as specifications.
Once you have established the list of pieces and parts, step through them and group them into logical categories. For example: seeds, dirt/planting media, wood, brackets and screws/nails. Move the list from its base form into these categories. This is looking more like the WBS.
Here’s another example: The typical book is arranged into specific categories of content. At its inception, there is only a desire to “write”. As the idea germinates, the author begins to envision individual chapters – each with very specific content. As the book grows and an individual chapter evolves, there may be multiple “segments” or subheading topics within the chapter. What you see developing is a WBS for a book and it will eventually grow to become the table of contents. Each chapter is listed and each subsection within the chapter is listed underneath. Eventually the chapters will be placed in a specific order of occurrence and the table of contents becomes a very clear example of specifications. If you read the book, you should be able to expect the content to flow from topic to subtopic and chapter to chapter.
This is how the work is broken down, or decomposed, into categories in preparation to be expanded into a schedule of all the work needed to produce the product of the project. The key error many project managers make is to miss something in building out the core list or items. The important factor relative to the Work Breakdown Structure is that, without it, you cannot accurately predict the schedule (time line) or the cost of the project.
For a very thorough discussion of the entire realm of Work Breakdown Structures, check this U.S. Department of Defense Guide: https://www.secnav.navy.mil/rda/OneSource/Documents/New%20MIL-STD-881C%20Work%20Breakdown%20Structures%20for%20Defense%20Materiel%20Items.pdf