Let’s play a word association game. Before we begin, clear your thoughts. Try to stay focused on this game only. Are you ready?
What comes to mind when I say and write the word taxonomy?
As mental models differ from person to person, I am reasonably sure that I will get many different answers. Information architects have word and image associations with the word taxonomy that others might not have. Computer programmers and Web developers might have different image and word associations than others.
And some people, if I were able to see their facial expressions, seem confused. They might not use this word in their daily work and personal lives.
With so many potential personal definitions of taxonomy it’s no wonder there’s confusion on how it applies to Web design. That’s why I’ll be walking through the concept and how Web professionals should apply it, in this column.
Though a commercial Web search engine is not a human being, and thus, does not have a personal mental model, we can see how Google might interpret the word. Here is what I see.
I performed a query for the word taxonomy. As Google does not know my context, the search results look like the following screenshot. At the top of search results, I am presented with a definition of taxonomy from Google’s Knowledge Graph and two search listings from Wikipedia.
Figure 1: Google’s current interpretation of the single query word taxonomy.
From these search results, Google seems to be telling searchers that taxonomy is classification. When I explore the content of these search results, I conclude that a taxonomy is a system for naming (labeling) and organizing things into groups that share similar characteristics.
Anyone who is charged with the tasks of organizing and labeling content on a website, regardless of context, is responsible for a successful (or unsuccessful) taxonomy. Many Web professionals encounter taxonomies an a daily basis without them realizing it. Their work might affect all or part of a taxonomy.
The goal of website taxonomy is to make content easier to find via browsing, searching and asking. A taxonomy should support task completion. Users (humans) as well as technology should be able to correctly interpret a taxonomy.
Everyday Taxonomies
We encounter taxonomies in our everyday lives. For example, one taxonomy is food groups, such as fruits and vegetables.
Look at the photo of a salad below. Which ingredients in the salad are vegetables, and which ones are fruit? Some of the answers might surprise you.
Figure 2: Do you see only vegetables in this salad?
Here is a partial list of fruits and vegetables, including some of the ingredients in this salad:
Items in this salad include fruits, such as tomatoes and cucumbers, as well as vegetables, such as lettuce and radicchio. Many people might not know that tomatoes and cucumbers are classified as fruit. Heck, I didn’t know that one of my favorite salad ingredients, avocado, is a fruit.
Other items in this table might seem strange. Another term people use for yam is sweet potato. So if I were working on a food or recipe site, I might want to use both of these words in website labels, such as:
Yam/Sweet Potato Recipes
Yam (Sweet Potato) Salad
How to Freeze Sweet Potatoes (Yams) From Your Garden
Likewise, mustard seems to be a strange item to see in the Vegetables category. Many people have a different mental model of mustard — it is a condiment that we might put on a hamburger or hot dog. If I used the term mustard greens in the Vegetables category, however, it might make more sense to people.
Remember, in a taxonomy, labels should be clear and distinguishable.
Figure 3: What is your mental model of mustard: a condiment or a vegetable? Is your mental model of mustard a bright yellow color, a green color, or some other color?
How about corn? Is corn a fruit, vegetable or grain? Corn is an odd food in that it can be classified in all three categories.
I show these examples to illustrate the different ways we might deal with taxonomies. We might have different mental models for the same label. We might use different labels for the same item. We might unknowingly miscategorize an item or multiple items. An item might belong in multiple groups.
What does this food example have to do with websites? Everything. Common issues with food taxonomy also occur on websites.
Types of Taxonomy
One pervasive misconception about taxonomies is that they always have a hierarchical structure. Though many websites can have a clear hierarchical structure, a strict hierarchy might not be the best way to organize and label content. Reason? User mental models often differ from the mental models of your marketing team, your technical team, and even your SEO (search engine optimization) team.
In other words, your marketing director might be able to easily find your site’s content, but your users might not.
When usability professionals and information architects conduct card-sort tests, they learn the different ways that people organize and label content. The taxonomy might be flat, as we commonly observe on smaller websites and parts of larger websites.
The taxonomy might contain both categories and facets, as we might observe on a large e-commerce site. As a form of error prevention and handling, cross references might be a part of the resulting site navigation.
To make content findable via all means (browsing, searching, asking), it’s critical to create and maintain a clear taxonomy. The four types of website taxonomies are: flat, hierarchical, network and faceted.
Flat Taxonomy
A flat taxonomy, also known as an unlayered taxonomy, is simply a list of items. A flat taxonomy has only top-level categories. In a flat taxonomy, the items are weighted equally, though on a website, it is common to put the most important item first on the list.
Figure 4: Representation of a flat taxonomy.
Small websites can have a flat taxonomy and be user friendly.
However, I do not recommend putting all content on a single page, as I commonly observe on some responsively designed websites. To communicate content “aboutness” to both users and technology (such as search engines), it is best to split content into separate pages.
For example, the About Us page should communicate information about your company or organization. The Contact Us page should show users how to contact your firm — both online and offline. Each page should have unique and descriptive titles, headlines, content and metadata.
Hierarchical Taxonomy
In the book Information Architecture for the World Wide Web by Louis Rosenfeld and Peter Morville, a hierarchical taxonomy is a hierarchical arrangement of categories within the interface of a website or intranet. It is often represented as a tree or a flowchart (see Figure 5 below).
Individual items within the hierarchy are arranged in order of importance or status. Moving up the hierarchy means expanding the category or concept. Moving down the hierarchy means refining the category or concept.
Figure 5: Representation of a hierarchical taxonomy.
The food taxonomy at the beginning of this article is an example of hierarchical taxonomy. Users are comfortable with hierarchies, as Rosenfeld and Morville explain:
“Hierarchy is ubiquitous in our lives and informs our understanding of the world in a profound and meaningful way. Because of this pervasiveness of hierarchy, users can easily and quickly understand websites that use hierarchical organization models. They are able to develop a mental model of the site’s structure and their location within that structure.” – Information Architecture for the World Wide Web, 3rd edition, p. 69
Not all hierarchies are simple, one-to-one parent-child relationships. Some hierarchies contain items that can be in multiple categories. Taxonomies that allow cross-listing are known as polyhierarchical.
Figure 6: Representation of a polyhierarchy.
Here are some general guidelines for presenting a hierarchical taxonomy:
Broad and shallow is better than narrow and deep. Though responsive design tends to focus on a deeper hierarchical structure, content is more easy to find and locate in a broad and shallow structure. Try not to sacrifice findability, as it is a critical component of the user experience.
Unique category labels. Category labels should be clear, concise and distinguishable to users. For example, Drug Abuse and Substance Abuse were presented to me as unique categories from an SEO firm, with separate content for each category.
However, during usability testing, participants did not understand the difference. They exhibited pogo-sticking behavior due to their confusion. Ultimately, they did not trust the site with the confusing taxonomy.
Don’t build different pages based on keyword research data and expect them to fit neatly into a hierarchical taxonomy that users understand.
Implement error handling and recovery in your taxonomy and content. Some users commonly look for an item in the wrong category (a frog is an amphibian, not a reptile; a turtle is a reptile, not an amphibian). And some users might not be familiar with an acronym. Because of these occurrences, you might want to build error prevention into your content, as shown in the site index of the U.S. Centers for Disease Control and Prevention.
Figure 7: A section from the U.S. Center for Disease Control Site Index that accommodates cross referencing and acronyms.
Network Taxonomy
A network taxonomy organizes content into both hierarchical and associative categories. Categories can be linked to any other categories. And relationships among items can have different meanings, including semantic ones. (See Slideshare by Denise Bedford, Taxonomies for Information & Knowledge Management Architectures.)
Figure 8: Representation of a network taxonomy.
Personally, I am a big fan of network taxonomies because the relationships among items are often more meaningful to users. I might start with a hierarchy and interpret that into global and local navigation. I will connect content in more meaningful ways (to users) in contextual navigation.
Examples of contextual navigation include:
Most popular
Most viewed
Most recent (for specific types of websites)
Alternatives
Upsells
Recommended reading
Contextual navigation can be curated and automated. Be careful about including too much navigation on a Web page. Too much navigation can easily overwhelm users and not support task completion.
Remember, too, that taxonomy is not navigation. A network taxonomy can seem unwieldy to users. If you know that your website is going to have a network taxonomy, I highly recommend working with a skilled information architect to ensure user-friendliness of the corresponding site navigation.
Facet Taxonomy
A facet taxonomy allows an item to be assigned to multiple taxonomies (sets of attributes), enabling the classification to be ordered in multiple ways, rather than in a single, predetermined order (as in a strict hierarchy). This definition is from one of my favorite books: Introduction to Cataloging and Classification by Arlene G. Taylor.
Let’s simplify this definition a bit by using an example website, Zappos.com. Suppose you want to buy a pair of walking shoes on the Zappos.com website. The different facets (sets of attributes) for women’s shoes are:
Size
Width
Performance (I think this is an odd label…it means what the shoe will be used for – like walking)
Brand
Color
Price
Performance shoe support type (another odd label)
Features
Insole
Shoe weight
So imagine, in Figure 9 below, that Women’s Shoes is in the center of the diagram, and all of these facets are ways that you can narrow down the type of shoes you wish to purchase.
Figure 9: Representation of a facet taxonomy.
We can even put Men’s Shoes in the center of the diagram, as these attributes are applicable to men’s shoes as well as women’s shoes. That is the idea behind a facet taxonomy. It’s not a one-size-fits-all approach to organizing content. A facet taxonomy allows users to locate and discover content based on the facets that are important to them.
According to Rosenfeld and Morville:
“Information architects and interface designers can experiment with hundreds of ways to present navigation options. The interface can be tested and refined over time, while the faceted classification provides an enduring foundation.” – Information Architecture for the World Wide Web, 3rd edition, p. 224
As much as I understand facet taxonomies, I encounter many problems with them on websites. These sites deliver duplicate content to Web search engines. Therefore, if I know a website is going to implement a facet taxonomy, I will be pro-active. I will do my best to manage duplicate content delivery as I am building and maintaining the site.
Second, a category page and a search results page are two different page types. Site visitors should know when they are using a site search engine (searching) and when they are browsing. But that is a whole other topic!
Creating and maintaining a successful taxonomy should be an important part of the website design, development, optimization and marketing processes. Make sure you are using the most appropriate taxonomy for your content.
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