If your site has thousands of pages of content that you’re struggling to organise, it’s pretty tempting to scrap your CMS-driven navigation structures and just provide your visitors with a search-driven interface instead. You can achieve this in two ways.

Firstly, by providing a simple search box. After all, this is the way most people find new information through Google. Secondly, by using a search tool to push similar content to users; for example the right-hand column of this page provides links to pages that are classified under different themes. But before you view search as some kind of panacea for all your information architecture woes, let’s pause to reconsider these two methods.

In the first case, how do you know that the search results presented by Google are the most relevant pages to your query? Google has no real benchmark. Then weigh up how much effort people put into ensuring their content is optimised to appear at the top of the search results and then ask yourself what you’d have to do to ensure that relevant content for every search a user undertakes.

In the second case, consider that actually I’ve already (very loosely) made decisions about navigation by tagging every post. This is almost the same effort as organising the content into folder structures as you would in a CMS. In fact, for sites with lots of content it can be more difficult to tag all the content than to drop it into a folder structure; the folders provide a more complete classification metaphor that’s easier for people with less expert knowledge to implement.
So how do you decide when search is better for navigation than in a CMS? Here are my suggested criteria:

1. You have the money.
   Implementing faceted search technologies can be significantly more expensive than using standard content management system functionality. Day rates for leading product professional services are often relatively high, there are licence costs and there’s an additional cost of integration, particularly if you need to tie a security model into the search tool.
2. You have few content types.
   But you have lots of content. Structured navigation from search works well where you have similar kinds of content, with similar structures against which the search engine can execute straightforward queries. A product catalogue is an obvious example. The tool can filter on price, format, location, etc. which have definitive and distinct values.
3. Your content is distinct.
   Categories need to be unique; semantic tools aren’t really advanced enough yet to tell you that apple is a fruit not an iPhone when displayed with orange unless orange is the network provider. Moreover, your pages need to be called something readily identifiable. If you have ten pages called “Help” or “Contact Us”, how will the search tool know which is the relevant resource for the site visitor?
4. Linking is obvious.
   If you use search to provide your navigation, you relinquish editorial control, so it must be clear why pages in the navigation are related. On a medical site, for example, you might link to other conditions treated with the same drug. However, as soon as you’re trying to tell people something you can get in trouble if you automate. An example I often use is a page about health advice for eggs: should this link to information about required protein intake (i.e. eggs are good for you) or about cholesterol (i.e. eggs are bad for you)? Or should you exercise some editorial discretion and explain about balanced diets? There are few search engines that could perform the navigation required to achieve the latter example.

Practically, it’s generally simpler to use CMS to navigate, with a search option to help people who are stuck. The advantage of CMS-driven navigation is that the editorial control you can exercise should help you to push visitors to your site along a route you want them to take. However, if you’re happy to let your intrepid visitors explore your content, and you’ve nothing in particular you want to promote to them, then search engines can be a viable means to provide navigation.

My final analogy is that CMS-driven navigation is like a library, while search-driven navigation is more like a bookstore. In a library you’ve preplanned how visitors can find specific information. In a bookstore you’re encouraging them to browse, but they may never find what they came in for.