he dilemma is common. Your web site starts out by design with a few pages
of content—a front page, a products page, perhaps something about the company or person putting up the site—and you can generally manage the various links on the site by hand. However, as the site needs to do more (and be more to its audience) its organization begins to unravel. You're soon spending all your time trying, rather desperately in the end, to stay on top of all the links being added and changed, and your nice, clean navigation system needs a higher level of organization. Single links become primary menus and subordinate submenus. Your user base begins to complain about how difficult it is to navigate around your site, and the number of bad links grows alarmingly.
You need a content management system (CMS), right? Well, yes, to a point. A CMS makes it a little easier to add resources and does a certain level of autoclassification, but at some point you realize that you're reaching a critical point where people aren't visiting vital places on your site, and you're spending all your time in triage mode.
As if that scenario isn't enough, your company's marketing director wants you to start developing a community for the site that will be able to post new resources: blogs, pictures, and video links. Soon you find yourself spending your time vetting images and trying to place them in the right folders, and you and your team are trying to keep up with the load that provides navigation to your site. You haven't seen your wife in far too long, and your child, who was taking baby steps last week, has just matriculated from college.
You're suffering from classification overload. This very common ailment strikes webmasters, in particular, because they are quite frequently the ones who are often tasked with building site navigation. Yet sometimes it's worth asking what exactly the users are navigating...it isn't really the site itself, except perhaps at the most mechanical layer. Instead, when users come to your site, what they are doing is navigating the information space that you have created. They're seeking categories and topics that are germane to their own interests, and in great part the degree to which they can move from one topic to a related one (for some arbitrary definition of related) determines how difficult it is for them to navigate the site.
Figure 1. Linear Taxonomy: The Rational Link associates an action with a given term in the taxonomy.
Descending the Pyramid: Hierarchical Classifications
Classification is an indispensable part of the process of building knowledge. As such classification systems have long been associated with areas such as library science or biology, but ultimately classification is a critical part of the way that we think about most things. To understand something new and to be able to extract both the similarities and the differences, you have to have some way of comparing it with things that are like it. If you have no basis for comparison, then making the leap to understanding is much harder, if not impossible. Such comparison is why writers create exemplars or why science instruction teaches the solutions to the easy problems first. Without the ability to recognize that a new problem is similar to an old problem (species, economic model, and so on) the problem becomes intractable.
The problem is that classification is, intrinsically, metadata; it is information about a given domain, rather than information that is inherently within that domain. This characteristic means, as one consequence, that there is no one definitive classification system (or taxonomy) that is exclusive to any one piece of information.
An object may have a single label in a linear taxonomy (see Figure 1); for example, calling a small, carnivorous quadriped with fur, a long tail, and a distressing tendency to leave birds on your doorstep a cat is one form of classification, but such a creature can also be called a member of the family Felidae, of the order carnivora, of the class Mammalia, of the phylum Chordata, of the Kingdom Animalia. These membership labels describe groups of increasing size, of which cats are members, and in this particular case each classification is also a member of the next, higher classification. This classification is thus referred to (or is classified) as a hierarchical taxonomy (see Figure 2).
Figure 2. Hierarchical Taxonomy: Parent-child relationships fold the taxonomy, implying scales of categorization. In some taxonomies the containment relationship migrates other actions; in others, it's possible for parents to maintain their own distinct actions in addition to being containers.
Hierarchies serve to assign common properties to the abstraction at the cost of detailed information from any given term in that taxonomy. Telling you that a cat is a chordate, for instance, informs you that it has a spinal chord that generally runs above or behind the primary organs (in opposition to gravity, generally), and because Phylum Chordata is also embedded within Kingdom Animalia it also inherits those things common to animals; namely, they are unable to generate energy from the sun and as a consequence must derive energy indirectly through the consumption of other living organisms, they are built using organic carbon compounds, and generally they are motile rather than sessile.
However, knowing that a cat is a chordate doesn't tell you anything to differentiate a cat from a dog or a dinosaur or a carp, which characterizes one of the flaws of hierarchies from a navigational standpoint. The criterion for membership within that classification must be clearly articulated, and should a given definition be established as erroneous, the potential number of members so affected by the classification can be huge (see the sidebar, "Evolving Biological Classifications").