Taxonomy is one of the least understood weapons available for SEO.  We all know the basics of effective SEO:

• URLs constructed with relevant terms, avoiding parameterization
• Each page can be accessed by only one URL
• Effective use of keywords in the title tag
• Use of keywords in H1 tags
• Links back to the page from other pages

How does taxonomy fit into all of this?

I started a webzine in 1998 called ProRec.com.  I built a custom CMS to run it, and spent a few years on SEO back before there was something called “SEO”.  In fact ProRec predates Google.  By the spring of 2000, ProRec consistently ranked in the top 10 search results on all relevant terms, usually in the top 3.  Due to many factors, some beyond my control, ProRec went dark in 2005 and was relaunched on DotNetNuke’s Blog module in 2007.  It no longer enjoys its former ranking glory, but I hope to use the lessons I learned to improve the Blog module in future versions.

One of the lessons I learned was the importance of effective use of taxonomy on SEO.  Designing and properly using effective taxonomy solves several problems:

1. Populates META tags appropriately
2. Encourages or enforces consistent use of similar keywords across the site
3. Forms basis for navigation within the site, linking related pages
4. Forms the basis for navigation outside the site, linking to other related information

Let’s look at these one at a time.

Populating META Tags

It’s true that META tags are not as important to search engines as they once were, but they are still used, and therefore still important.  Most blogging systems will take the keywords entered as Category or Tags and use them as META tags.  If you’re using DotNetNuke’s blog module, however, you’re out of luck.  The system simply doesn’t comprehend any kind of taxonomy and doesn’t let you inject keywords into the META tags except at the site level.  Opportunity missed.

When it comes to content tagging, a structured taxonomy (categories) offers benefits over ad-hoc keywords (tags).  The obvious reason is that a predefined and well-engineered taxonomy is more likely to apply the “right” words since a user manually entering tags on the fly can easily be sloppy or forget the appropriate term to apply.   The less obvious reason is that as a search engine crawls the site, it will consistently see the same words over and over again used to describe related content on your site.

Why is it important for the search engine to see the same words over and over again?  Because “spray and pray” (applying lots of different related words to a given piece of content) doesn’t cut it.  You don’t want to be the 1922th site on 100 different search terms.  You want to be the #1, #2, or #3 site on just a few.

So think of a search engine like a really stupid baby.  Your job is to “teach” the baby to use a few important words to describe stuff on your site.  Just like teaching a human, the more consistent you are, the more likely the search engine is to “learn” the content of your site and attach it to a small set of high-value terms.

Enforcing Keyword Usage

One of my main complaints about “tags” versus “categories” is that tags added to content on-the-fly tend to be added off the top of one’s head.  That’s fine for casual bloggers who just want to provide some simple indexing.  But if you are a content site with a lot of information about some particular subject, chances are that tagging like this can get you into trouble.  The reason for this is because on-the-fly tags often inadvertently split a cluster of information into several groups because two or three (or more) terms will be used interchangeably instead of just one.

Consider a site with a well-defined and structured taxonomy.  Let’s consider a very common application: a photography site primarily covering reviews of cameras and photography how-tos.  A solid taxonomy structure would probably include four indexes:

• Manufacturer (Canon, Nikon, Lumix, etc..)
• Product Model (EOS, D40, TZ3, etc..)
• Product Type (DSLR, Rangefinder, micro, etc..)
• Topic (Product Review, Lighting, Nature, Weddings, etc..)

Generally, the product reviews would be indexed by manufacturer, product model, and product type, with the “Topic” categorized as “Product Review”.  How-tos would be indexed by their topic (“Weddings”) as well as any camera information if the article covered the use of a specific camera.  For example, an article called “How to Improve Low-Light Performance of the Lumix TZ3” might be indexed thusly:

• Manufacturer: Lumix
• Product Model: TZ3
• Product Type: Compact Digital
• Topic: High ISO

Having a system that prompts the user to appropriately classify each article ensures that the correct keywords will be applied.  Getting the manufacturer and model correct is probably pretty easy.  It’s harder to remember the correct product type (“Compact Digital” versus “Compact”).  And remembering the right topic is a real challenge (“High ISO” versus “Low Light” versus “Exposure” or any of a hundred other terms I could throw at it).  Moreover, the user must to remember to apply all four keywords when the article is created.

We can see the value of focused keywords from this example.  At a site level, relevant keywords are at a high abstraction level, like “camera review”.  It’s unrealistic to think a web site could own a top search engine ranking for such a broad term.  At the time of this writing, Google shows almost 14 million web pages in the search result for “camera review”.  But a search for the new Nikon laser rangefinder “nikon forestry 550” returned only 138!  An early review on this product with the right SEO terms could easily capture that search space.

Having a system with four specific prompts and some kind of list is essential to keeping these indexes accurate.  Ideally the system provides a drop down or type-ahead list that encourages reuse of existing keywords.

Creating a Navigation System

Here’s where it all starts to come together.  Once you have a big pile of content all indexed using the above four indexes, the next obvious step is to create entry points into your content based on the index, and to cross-link related content by index.

On ProRec, we had five entry points into the content:

• Main view (chronological)
• Manufacturer index
• Product Model index
• Product Type index
• Topic index

Needless to say, when a search engine finds a comprehensive listing of articles on your site, categorized by major topic, it greatly increases the relevance of those articles because the engine is able to better understand your content.  Think about it: right there under the big H1 tag that says “High ISO” is this list of six articles all of which deeply cover the ins and outs of low-light photography.  It’s a search engine gold mine.  Obviously it also helps users navigate your site and find articles of interest, too.

My favorite part of the magic, however, was using the taxonomy to create a “Related Articles” list on each article.  Say you’re reading a review of a Lumix TZ3.  We can use the taxonomy to display a list of articles about other Lumix cameras as well as other Compact Digital cameras.  On ProRec this was even more valuable, because ProRec reviews (and how-tos) many different types of gear and covers a lot of different topics.  Go to a review of a Shure KSM32 microphone, and here’s this list of reviews of other mics.

The “Related Articles” list immediately creates a web interconnecting each article to a set of the most similar articles on the site.  Instantly the search engine is able to make much more sense out of the site.  And, of course, readers will be encouraged to navigate to those other pages, increasing site stickiness.

More SEO Fun with Taxonomy

Once the system was in place I was able to extend it nicely.  For example, I created a Barnes & Noble Affiliate box that used the taxonomy to pull the most relevant book out of a list of ISBNs categorized using this same taxonomy and display it in a “Recommended Reading” box on the page.  So you’re reading an article called “Home Studio Basics” and right there on the page is “Home Studio Soundproofing for Beginners by F. Alton Everest” recommended to you.  The benefit to readers is obvious.  But there are SEO benefits, too, because search engines know “Home Studio Soundproofing for Beginners by F. Alton Everest” only shows up on pages dealing with soundproofing home studios.  Pages with that title listed on them (linked to the related page on Barnes & Noble) will rank higher than those that don’t.

You can start to see how quickly a simple “tagging” interface starts to break down.  You need the ability to create multiple index dimensions (like product, product type, and topic) as well as some system to encourage or enforce consistent use of the correct terms.  Otherwise, you’re doing most of the work, but only getting part of the benefit.

Taxonomy, Blogging, and DNN

Obviously, most casual bloggers don’t want to be forced into engineering and maintaining a predefined taxonomy.  That’s why “tagging” became popular.  Casual bloggers want to be able to add content quickly and easily and anything that makes them stop and think is a serious impediment to workflow.  So you just don’t see blog platforms with well-engineered categorization schemes, and you definitely don’t see any that allow for multiple category dimensions.

In my article “Blog Module Musings” I wondered aloud about what sort of people really use DotNetNuke as a blogging platform in the traditional sense of the word “blogging”.  My guess is that most people using DNN as a personal weblog probably have some personal reason for choosing DNN instead of any of the free and easy tools readily available like WordPress or Blogger.  So I have a belief about DNN that it isn’t a good platform for a “blog” per se, but it’s a great platform for content management and publishing.  My guess is that the DNN Blog module has much greater utility as a “publishing platform” instead of a “personal weblog”.

As such, I think it makes sense that DNN’s publishing module should offer more taxonomy power than the typical blog.  I also think that it’s possible, using well-designed user interfaces, to make a powerful taxonomy easy to manage.  My experience with ProRec demonstrated this.  It was very easy to manage ProRec’s various indices, primarily because I had a fat client to provide a rich user interface.  With Web 2.0 technologies, we can now provide these user experiences in the browser.