PLM, product structure and multi-level BOM. Let’s sort it out…

PLM, product structure and multi-level BOM. Let’s sort it out…


One of the complex topics in product development and manufacturing is multi-level BOM. Very often, multi-level BOM is presented as an important functionality supported by PLM systems in comparison to management of BOM using Excel spreadsheets or sometimes even ERP systems.

Here is Wikipedia definition in Bill of Materials article:

A Multi-Level Bill of Materials (BOM), or referred as an indented BOM, is a bill of materials that lists the components, assemblies, and parts required to make a product. It provides a display of all items that are in parent-children relationships. When an item is a sub-component, unfinished part, etc., all of its components, including finished parts and raw materials, are also exhibited. A multi-level structure can be illustrated by a tree with several levels. In contrast, a single-level structure only consists of one level of children in components, assemblies and material.

Autodesk PLM blog – What should be included on the Bill of Materials brings the following passage explaining if you should manage BOM as a flat of hierarchical structure.

Will the BOM be flat or hierarchical? Sometimes, companies like to manage the BOM so that parts within a certain assembly are grouped together under their parent, which creates a hierarchical BOM. This can make certain management tasks easier, but adds to the overall complexity, particularly if a company is using Excel for their BOM management strategy. A flat BOM, where everything is given the same priority, might be good for electrical engineers and for simpler management, but it doesn’t allow for complex relationships between products and makes working with contract manufacturers slightly more complex.

Another article from Arena PLM – Managing multi-level BOMs brings some additional definition points about managing of multiple level BOMs and Arena’s capability to stand for such requirement.

Choosing which BOM Structure to Use. To define the BOM structure that best suits your needs, it is important to consider who will be using the BOM as well as the type of product you build using the BOM. Ask yourself the following questions. Will your BOM be used in-house for engineering purposes? Will your BOM be shared with a contract manufacturer, partner or other collaborator? What types of products do you make? What is the complexity and configurability of your products? These are just a few important factors to consider when structuring your bill of materials

How Arena PLM Helps Manage Multi-Level BOMs. Arena PLM, bill of materials and change management, offers a more efficient approach to managing multi-level BOMs than Excel. Because the software is built on a relational database, you can create an unlimited number of one-to-many and many-to-many relationships, which prevents data entry mistakes and eliminates product data ambiguity. You can also mass replace a single part in several locations within a BOM or in multiple disparate BOMs—saving hours of time and eliminating BOM discrepancies.

Multi-level BOM is often confused with product structure. In the past, I’ve been asked a lot about what is a difference between these two things, in what situations to single BOM vs multi-level BOMs and How many levels should be in a BOM? Here is my take… But I also want to hear your definitions and opinions as well. So, don’t be shy if you disagree :).

Multi-level BOM is a way to organize multiple single level BOMs together based on a specific breakdown structure. There are different reasons why organizations of BOM into multiple-level can be very helpful. Multiple BOM levels can represent a certain way of managing BOM. The way levels (hierarchies) are organized can reflect structure of product, configurable modules, supply packages, manufacturing processes and many other aspects. It is important to remember that each “level” is a separate (single-level) BOM identified in the manufacturing system of record by Part Number and sometimes additional parameters (e.g. revision).

Product structure is a hierarchy of product (parent-child relationships). Product structure is a three (or graph) of relationships between parts and assemblies representing product itself. Some multi-level BOMs (especially engineering BOM) can reflect product structure  when it comes to relationships between assemblies, sub-assemblies and parts. But multi-level BOM is a broader definition and can represent other data as well in manufacturing, supply chain, etc.

What is my conclusion? Terminology is a complex thing in engineering and manufacturing. You ask 2 engineers the same question and end up with 3 answers. So, here is my take on multi-level BOM and product structure now. Multi-level BOM and product structure are related, but this is not the same. Muti-level BOM can represent processes in multiple areas of product development – engineering, manufacturing, supply chain, support, etc. I can be used to create product configuration modules, assembly instructions as well as to structure supplier collaboration. Product structure is a representation of part-child relationships in the way assembly and components are coming together in a product. It can represent design or physical product. Just my thoughts…

Best, Oleg

Want to learn more about PLM? Check out my new PLM Book website.

Disclaimer: I’m co-founder and CEO of openBoM developing cloud based bill of materials and inventory management tool for manufacturing companies, hardware startups and supply chain. My opinion can be unintentionally biased.


Share This Post