In our work of building and maintaining e-commerce taxonomies, we often run into the problem of products not fitting nicely into one single category. Although this problem is not specific to e-commerce taxonomies, their use for navigation and browsing presents a special categorization challenge; the need to lead a wide range of customer types down an intuitive path to the product they are looking for.
Think about something as simple as a pair of headphones: where do they belong in the following hierarchy?
- CD Players
- MP3 Players
- Home Theater
- Stereo Receivers
First of all they are an audio product, so from a purely taxonomic standpoint they could exist as a direct child of audio. However if there is one thing we know from endless hours of user testing, its that people love accessory categories and anytime you ask them to find a product that is small in size they will immediately gravitate to accessories.
Ok, so what if we put them under audio, and then, under audio accessories. Great, but people often look for products in categories which they feel are related in more abstract ways. For example, it is not uncommon for users to say things like:
“I Iisten to my MP3 player with headphones so I would look there”
Now imagine other branches of the taxonomy such as Computers or Video Game Consoles. There are lots of headphones made specifically to work with these types of products. Do we place headphones there as well?
I am sure you are starting to get the idea, headphones are becoming ubiquitous in our taxonomy, but is that a problem?
There is no real hard and fast rule or best practice around polyhierarchy. It is an important part of the taxonomists’ toolbox and an essential feature of navigational taxonomies. However in our quest to accommodate a wide variety of users and achieve maximum findability, it can easily be overused.
One of the biggest dangers of overused polyhiearchy is that the principles that govern the framework of the taxonomy become diluted. This can result in the placement of products in categories based on overly abstract associations, and can lead to a whole slew of governance problems as the taxonomy evolves.
Another problem with polyhierarchy has to do with its implementation on websites. In some e-commerce applications of content management, polyhierarchy is achieved through a single master location of a given product that gets linked to from other locations in the taxonomy. This can lead to some very disjointed navigational experiences, especially when the polyhiearchical treatment involves multiple branches of the taxonomy.
For example if the master location of headphones is as a child of Audio, then the following pathway could be possible
Computers > Computer Accessories > Headphones
(select and be directed to a new breadcrumb trail)
Audio > Headphones
All of a sudden the user finds himself in an entirely different branch of the taxonomy. This can be a jarring experience that detracts from the learnability of the taxonomy structure.
The next question then is: does the average user really care? I would argue that most users are more concerned with finding products than the purity of the navigational pathway involved. They can always resort to the ever present “back” button.
That being said, the best way to determine where polyhiearchy should be used is with user testing. Products that are candidates for polyhierachy should be tested with a broad spectrum of users. Analyzing their chosen access points into the taxonomy will give you a clearer idea which associations warrant polyhiearchy and which ones do not.
As a general rule we tend to err on the side of too much polyhiearchy, even though our taxonomist spines may shiver at the thought of some navigational pathways. At the end of the day our goal is to help people find what they are looking for. If that means including headphones in computer accessories… so be it.