Product Taxonomy Mutual Exclusivity - One Product, One Place

Mutual Exclusivity is an organizing principle for taxonomies which requires every SKU in your product catalog have one (and only one) place in the product taxonomy. 

A taxonomy is the collection of categories that represent the products you sell on your website and shows they relate to other types of products in your selection. 

Because taxonomies are built around product categories, they are designed such that each SKU can be filed under only one category. This concept of “each item can be classified to a single product category” is what defines Mutual Exclusivity.

Here is a simple thought experiment to illustrate the concept.  Imagine two online stores where lemons are sold.  In store A, you see:


  • Fruit
    • Citrus Fruit
    • Melons
    • Apples

It is easy to guess that Lemons, being a citrus fruit, would be found under Citrus Fruit.  They are Citrus Fruit and they are not Melons, nor are they Apples. Each SKU of Lemons that you sell would then be classified to the “Citrus Fruit” category. Obvious and helpful, right?

Now consider this taxonomy structure for store B:


  • Fruit
    • Citrus Fruit
    • Yellow Fruit
    • Sour Fruit

This is problematic – Lemons are Citrus Fruit, but they are also Yellow Fruit and they are Sour Fruit. So in this structure Lemons could be placed in any one of these categories.  This store has violated Mutual Exclusivity by creating multiple categories where a Lemon SKU could (correctly) be assigned. 

PRO TIPS: How Product Attribute Schema Design Works As A Competitive Advantage

Why does mutual exclusivity matter?

It might seem obvious with lemons – who would create a “yellow fruit” category?  Yet we see the second scenario frequently with ecommerce sites. 

When you have a LOT of SKUs to organize the problem is much more complex. 

But with more products to browse your organizing principles impact the experience of the buyer to an even greater degree.  So, mutual exclusivity is a golden rule that you must not break.  Here are some solid reasons:

  • When a product is found in more than one category, customers have to go multiple places on your site to see the full selection – this adds effort to product discovery and can negatively impact a site’s effectiveness.   People are busy.  When they get frustrated enough with digging through category after category, eventually they will give up and go elsewhere. 
  • Poor categorization reflects poorly on your company.  If your categories aren’t Mutually Exclusive, frustrated users may question your expertise - do you really know anything about what you are selling? Are you the right place for them to purchase this product?  You may lose not only that prospect but others they tell about your siteShow you know what you are doing by organizing wisely.
  • Governance of your product data is much simpler with a Mutually Exclusive taxonomy, as it ensures all SKUs of a particular type are managed together in a single home with a single set of rules for data quality.
  • New item launches and sharing data with partners and suppliers are much easier when they can pair each of their categories with a single (Mutually Exclusive) category in your taxonomy. A 1:1 match between your taxonomy and your channel partners reduces time to launch and encourages your suppliers or distributors to carry more of your line.

What to do right now

Consider doing a “Store Walk” through your taxonomy from the point of view of the personas who would visit and purchase from your site. 

  • What kind of products are they looking for? 
  • Is it clear which categories they should choose to find each one? 

This exercise will likely lead to some valuable ah-ha moments regarding your site navigation and give you a path to improvement. 

Look at your Product Detail Pages as well.  The information displayed there can also be impacted by Mutual Exclusivity.  If your taxonomy is not mutually exclusive then you may have SKUs of the same product type appearing in multiple categories where different specifications are shown – making comparison difficult.

This can happen when the duplicate categories have different requirements for attribution (which can happen when duplicate categories exist).

Resolving this by combining the duplicate categories into a single Mutually Exclusive master category improves the user experience by making it easy to compare “apples to apples” in one place.  Be sure to add comparing like items as part of your “Store Walk” exercise.

What to do going forward

If you have a site already test for mutual exclusivity and fix what’s broken.  Have your product managers conduct “Store Walks” to look for issues.

If you haven’t built your site yet,  now is the perfect time to plan to build with mutual exclusivity in mind – before you waste money on site designs or wireframes.

Review your site regularly, and refine your taxonomy to keep it compliant as you grow.  Disorder has a way of creeping in if you aren’t paying attention.  Be sure to vet new items so that they fit into one, and only one, category; if you “bend” your categories (classifying SKUs there that don’t genuinely belong) you are only making more work in the near future.

Learn how we use customer data models, product data models, content models, and knowledge architecture to create a framework for unified commerce download our whitepaper: Attribute-Driven Framework for Unified Commerce

Meet the Author
Earley Information Science Team

We're passionate about managing data, content, and organizational knowledge. For 25 years, we've supported business outcomes by making information findable, usable, and valuable.