Categories, Tags, and Taxonomies in WordPress

When I upgraded my Hedden Information Management website to WordPress a few months ago, I took advantage of WordPress’s blog post feature and incorporated a copy this blog into the website (while also keeping its original location on Blogger.com). The difference between categories and tags in the different platforms became clear. Blogger.com offers only “labels” to its bloggers, although these are listed as “Categories” on the displayed blog. WordPress, by contrast, offers both “Categories” and “Tags.”  When I imported my blog posts to the WordPress site, the Categories in Blogger.com became Categories in WordPress, but none of the posts had any Tags. I then realized that some of these Category terms perhaps should be changed to Tags.

The difference between Tags and Categories is a topic I blogged on five years ago.  A simple comparison is that Categories tend to be broader than tags, and more documents get assigned the same Category, whereas Tags tend to be more specific with fewer documents assigned the same Tag. Conversely, a document typically has only one or two Categories but more Tags.  Categories can also be organized into a hierarchy with subcategories, but Tags tend to be unstructured.  However, Blogger.com does not offer the capability of putting its Categories into a hierarchy, which would be desirable, since the number of my Categories has become too great to browse easily in a flat list.

WordPress appropriately treats Categories and Tags in differently in the following ways:

• Categories, unlike Tags, have the capability of being put into a hierarchy, be selecting a “parent” Category for a given Category. The hierarchy displays both in the Dashboard and optionally on the site.
• While both Categories and Tags are displayed on each individual post (and are hyperlinked to a list of posts which share the same Category or Tag), and both Categories and Tags that can be generated as Tag Clouds, it is only the Category list that can be alphabetically browsed by the site visitor (if added as a widget to a page).
• Categories are required, whereas Tags are not. If you don’t assign a Category to a post it will automatically get assigned the “Uncategorized” Category.
• Category labels appear additionally within the default URL of the blog post in a file path between the domain name and the filename. For example, my blog post with the Category of “Metadata,” received the URL of www.hedden-information.com/metadata/metadata-and-taxonomies.
• The Category name also appears within the breadcrumb trail, if the site has one displayed on each page. Of course, some blog posts have multiple Categories, and only one of them can appear within the URL and breadcrumb trail, so WordPress assigns one of them by default.

Creating and managing Categories and Tags for posts is a default feature of WordPress that’s easy to do in the Dashboard of a site. Since I had recently imported dozens of blog posts that had Categories and no Tags, I especially liked the feature to selectively convert Categories to Tags (One can also convert selected Tags to Categories.)  I went through my list of Categories and converted most of those that were infrequently used into Tags. The Categories to Tags Converter is one of the default Tools available for Import, but it does need to be “imported” and “activated” to be available.

Additional features in taxonomy management in WordPress can be obtained through various free or premium plugins. This is the case if you want to create multiple taxonomies, whether as sets of Categories or Tags, or faceted taxonomies. The default Categories and Tags feature permits the creation of just a single Category set and a single Tag set. If your site has different types of posts, such as custom post types, or if you want multiple term sets by which to filter posts by different aspects (facets), then you would need to create custom taxonomies. It is possible to create custom taxonomies by writing code, but if you are not a WordPress developer, there are plugins available for creating custom taxonomies. The support of synonyms/alternative labels/nonpreferred terms for Tags is also a feature available only with plugins, in this case plugins that aim to support search.

I will be discussing these topics in a presentation “Taxonomies,Categories, and Tags” at the WordPress conference, WordCamp Boston 2018, on Saturday, July 21. If you are in the Boston area come join me!

One or More Taxonomies

In the various definitions of taxonomy, one aspect of the definition that is often missing is what constitutes a single taxonomy (or thesaurus) versus multiple related taxonomies (or thesauri). If you hire a taxonomy consultant, they won’t tell you because they will defer to their client’s terminology. If you are designing a taxonomy/taxonomies for your own organization, however, this is often an issue of concern.

Hierarchies and other relationships

In simple hierarchical taxonomies, a single hierarchy could be a single taxonomy. Not all terms on the same subject, however, may fit neatly in one hierarchy while complying with ANSI/NISO hierarchical relationship guidelines. So, more often than not, a hierarchical taxonomy may have multiple top terms. For example, a taxonomy on health care might have top terms for hierarchies on conditions and diseases, diagnostic procedures, treatments, medical equipment and supplies. If for some reason you needed a single hierarchy, then you would bend the hierarchical-relationship rules to make such top terms narrower to the term that is the name of the taxonomy. Thus, whether there is one top term or multiple top terms, it is still considered one taxonomy.
Facets are a special case. Each facet consists of its own hierarchy of terms, or may even have multiple top-term hierarchies of similar-type terms on the same subject, and there are no relationships between terms in different facets. So, you might consider each facet to be a taxonomy. However, the facets are intended to be used only in combination, not in isolation. In fact, we often speak of a “faceted taxonomy,” implying a single taxonomy comprised of multiple facets. So, a single facet is not a taxonomy.

A more thesaurus-like structure, may have fewer large hierarchies and more smaller hierarchies with more numerous top terms, but it will also have associative relationships that link terms across hierarchies. So, a possible definition of a taxonomy or thesaurus is a set of terms where there is at least some kind of relationship between every term and at least one other in the same set. However, you could end up with a situation of just a couple of terms related to each other but none of them are related/linked to any other terms in the taxonomy. So, additional criteria are needed to define a single taxonomy as to include such terms.

Thus, at a minimum, a taxonomy comprises one or more hierarchies, but what about at a maximum? The question came up in my online course, in an assignment to create polyhierarchies, in which I suggest that the broader terms are from different hierarchies. A student asked: “Are the different hierarchies supposed to be within the same Taxonomy, or merely two different hierarchies from two different Taxonomies?” Generally, standard hierarchical and associative relationships do not transcend multiple taxonomies. An exception would be instance-type hierarchical relationships between topics in a taxonomy and named entities (proper nouns) maintained in a separate controlled vocabulary. Other types of relationships may link terms across multiple taxonomies, but they would likely be special-purpose relationships, such as equivalency mappings or translations.

Subject scope and purpose

In addition to considering the relationships between terms, another determining factor of what constitutes a single taxonomy is the subject area scope. One taxonomy is for one subject area, although that subject area could be very broad, especially if the taxonomy’s purpose is to support indexing of the topics in a daily national newspaper. More often, a taxonomy is more limited in scope, such as just technology topics or health topics.

Related to subject scope is how the taxonomy will be used in both indexing/tagging and retrieval. Generally, a single taxonomy is utilized in a single indexing/tagging method and with its own indexing policy. Policy, comprising both editorial style for terms and indexing rules, is often a defining factor for a single taxonomy. Different taxonomies will have different policies. For the end-user, a retrieval function is served by a single taxonomy, such as supporting a search function or providing a set of browse categories. If you want to enable multiple unrelated methods of retrieval (such as type-ahead for the search box, dynamic filtering facets, and a navigational browse), then you will need to create separate taxonomies for each. At a former employer I built taxonomies for SharePoint, and it turned out that I had to build three completely separate taxonomies: (1) the consistently labeled hierarchy of libraries and folders, (2) terms and their variants to support search with a third-party auto-classification tool, and (3) controlled vocabularies of terms for consistent tagging and metadata management of uploaded documents.

There is also the question of whether the content to be accessed by the taxonomy is together in one set or separated out for different purposes or different audiences. A taxonomy should be designed to suit its own content. This was the case in a current project I am working on. There are two distinct sets of content available on a web site. The content sets have many similarities, so could be browsed via the same one hierarchical taxonomy, but they are for potentially different audiences. If the content set were to remain separate, we would have created two separate taxonomies, each customized to best suit its own set of content. But the site owners decided that the two sets of content would be presented together, “blended,” to cross-sell content, in addition to standing on their own elsewhere on the site. Thus, a single taxonomy was the chosen option. The use of two content categories for terms within the taxonomy will enable the additional, separate content set option.

Conclusions

In sum, a single taxonomy:

• Has standard relationships (BT/NT, RT, USE/UF) confined within it. Cross-taxonomy links, if any, are of non-standard types.
• Has a defined, restricted subject scope.
• Has its own indexing/tagging policy.
• Could function in isolation, unlike a single facet (although may be supplemented by other controlled vocabularies/metadata).
• Has its own implementation, function, and purpose (although taxonomies can be reused and repurposed).

It’s important for a taxonomist to determine what constitutes a single taxonomy versus multiple taxonomies, not so much for communicating with stakeholders, but rather to plan the initial design of the taxonomy within a taxonomy management tool. Taxonomy/thesaurus software allows for the designation of one or more taxonomies/thesauri that may be linked to each other or not. The use of multiple so-called files, thesauri, vocabularies, objects, classes, categories, etc. are different ways that the various software tools allow the taxonomist to control the divisions between and within taxonomies.

Tags and Categories

What does a taxonomy comprise and how does it work? Professional taxonomists may speak of “terms,” “nodes,” or “labels,” whereas most other people with a basic understanding of taxonomy might refer to “tags” or “categories.” A category is a well understood concept, and social media sites have made the notion of “tag” well known.

In addition to the different professional level of such jargon, there is also a distinction in meaning.  Ironically, it’s the professional terminology that is vague and the layman terminology that is more specific. Taxonomy “terms,” “nodes,” or “labels,” are all pretty generic and can all have various applications for different kinds of taxonomies, both for broad categorization and for specific indexing. “Tags” and “categories,” on the other hand, each tend to have distinct meanings. It’s not so much what they are, or even how they are organized, but rather how they are used.

Tags are for tagging.
That seems obvious. As for what is meant by “tagging,” that implies you put a tag on something. In fact, you can put more than one tag on something, and that’s typically encouraged in tagging. “Something” is typically an electronic file of some form of content, a document, image, video, database record, blog post, etc. Tags tend to be a brief label indicating what something is about. Tags can be very specific or relatively broad. Information professionals might prefer to call them “index terms.” An organized, alphabetized list of tags could serve as an index.

Categories are for categorizing.
This can also be called grouping or classifying. It implies putting something into a category, often represented as a file folder, whether an actual electronic folder path, or just a depiction of a folder icon. While categories have different levels of specificity, the name category implies a collection of things, so there is an implicit understanding that categories don’t get too specific. An organized structure of categories typically constitutes a hierarchical taxonomy.

Can something go into more than one category? In physical folders no (unless you make photocopy of the document for each folder), but in the digital world, often the answer is yes, but not always (again requiring the copying of files). It depends on the system, and it may involve some workaround. Even when it is possible to put a content item into more than one category, unlike tags, it is still preferable to have most content items assigned to only one category and a smaller number of them that may belong in two categories. For example, there may be a breadcrumb trail for the hierarchy of categories, and the breadcrumb trail may only take a single path. The idea is that the categories retain distinct meaning and usage through mostly distinct content.

Tags and categories together
Because tags and categories are different, it is possible to have both at the same time, especially if the categories are deliberately kept broad and the tags are relatively specific. Content management systems and digital asset management systems increasingly offer features of both categories and tags for managing content. In these cases, the challenge is to decide to what degree of classification to use the categories and to what degree to use the tags. That's exactly what I have done as a taxonomist on two recent consulting projects.

For the amateur taxonomist and indexer, one of the most common exposures to tags and categories is through blogs. Blogging software may permit the blog author to assign a tag or category to a blog post.  Whether the tags and categories are appropriately named and used is another issue, though. Blogger.com provides only one option, which it calls "Labels" and utilizes an icon for a tag in the blogging interface, but then displays them when published in the right margin under a heading called "Categories."  No wonder my "categories" don't look good; I had created them as if they were tags. Furthermore, the very specific subject matter of "The Accidental Taxonomist" blog makes its posts more suited for tagging than for categorizing. WordPress, on the other hand, gives the blogger both tools: tags and categories. If “The Accidental Taxonomist” blog eventually moves, you’ll know why.