Dougal Campbell's geek ramblings

Since the upcoming WordPress 2.3 release will debut the new tagging system, I thought I’d take some time to address what it means to use “tags” versus using “categories”. These things mean different things to different people, as it’s really just a matter of how you want to use them. But let’s examine what tags and categories are, how they are similar, how they are different, and why you might choose to use one system over the other, or use them together.

What are categories?

A dictionary definition of category is, “A specifically defined division in a system of classification.” If you break that down, and consider what is meant by “a system of classification”, you’ll come to the conclusion that this refers to a highly structured, possibly hierarchical system. For example, to borrow from the classification system for living things, you might have a tree like “Animals -> Vertebrates -> Mammals -> Horses”. Any of those terms could be considered to be a category, and they fall into a strict structure.

What are tags?

In their most common usage, tags are keywords that you attach to a piece of content. Tags are “free-form”, which is to say that there is no formal restriction on what tags you attach. So, the basic difference between categories and tags is that categories are structured and tags are unstructured. For examples of popular web services that make good use of tags, see Flickr, Technorati, and Delicious, among others.

On the other hand, the help pages at Technorati define tags thusly: “Think of a tag as a simple category name. People can categorize their posts, photos and videos with any tag that makes sense.” They’re saying that tags are categories — so, are categories and tags different, or not?

How are categories and tags different?

If a tag can be thought of as a category, then how are they different? It really just comes down to how you use them. Typically, as we mentioned above, category systems are structured. In a given system, the categories are usually chosen with as little overlap as possible. Look at your typical mainstream news site — you’ll probably see categories like Politics, Business, Entertainment, Sports, Technology, and Lifestyle. The breadth of these categories covers just about any imaginable news story.

The problem arises when a story does overlap multiple thematic categories. What if you have a story about iRobot’s newest model of Roomba robotic vacuum cleaner — do you file it under Business, Tech, or Lifestyle? In many systems, you can assign multiple categories. But even in that case, there are often reasons to specify a primary category. Slashdot is a good example — if you look at their main page, each story has a single icon which represents the primary category. This is a quick visual indicator which helps you identify stories that might interest you. Then, if you click into a specific article, you’ll see the icons of other categories that the story fits into.

And in a strict category system, visitors using your search feature might use terms that don’t appear in the content or category names. What if Alice was trying to find the Roomba story, but couldn’t remember the name of the device or its manufacturer? She might try a search for “gadget”, or “carpet”, but maybe those terms were never in the story. This is where tags can help refine searches by giving additional keywords. If our story had tags like “business, technology, tech, lifestyle, gadget, floor, carpet, vacuum, cleaning, household, home, robot, robotics” and other relevant terms, then there are lots of extra hooks for searches to latch onto.

Which should I use?

There are some people who have discarded the hard structure of categories in favor of the free-form nature of tags. There are a few folks who prefer the clean thematic separation of a category system, and avoid the messiness of inconsistent tags. But most folks should feel free to get the best of both worlds. A while back, I started using my categories as tags. I create new categories on the fly, as seems fit. But I’ve gradually started to regret that decision. What I really wanted was to have both a category to specify the overall main theme for each post, and a set of tags to aid in searching.

In WordPress prior to version 2.3, the “category” system could be used as a “tag” system simply by the nature of how the user chose to express them. The difference was simply a matter of semantics. The same holds true with the new tagging system in WP 2.3, really — it’s all a matter of how you choose to use the underlying system. But the availability of a flexible taxonomy system now provides a way to clearly delineate a separation between “categories” and “tags”, and even user-created tertiary categorization systems. Previously, this type of flexibility was only possible through third-party plugins.

Whether you choose to stick with distinct categories, tags, or a combination of both, is really a matter of your personal preferences. But whichever path you choose, WordPress will be able to give you the tools you need to organize your content the way that you like.