Faceted Classification
Faceted classification is a hallmark of the bottom-up approach and suggests yet another reason why the phrase "build the taxonomy" is ill-conceived. Inspired by Yahoo and encouraged by portal software vendors, many Web and intranet managers have embarked on a long, painful, and doomed journey to build a single, all-purpose enterprise taxonomy. In a world where sites grow but budgets shrink, these monolithic top-down taxonomies will eventually be exposed as unwieldy and unusable.
The bottom-up approach suggests a very different way to classify content. When populating a top-down taxonomy, the central question is "where do I put this?" but at the heart of the bottom-up approach is the question "how do I describe this?" By asking this subtly different question, you'll wind up in a dramatically different destination. Where the top-down question evokes a single answer, the bottom-up question suggests many answers. You may describe a particular document according to any or all of the following categories:
- Topic What is this document about? What are the major subjects?
- Product Which of our products is featured in this document? How about our competitors' products?
- Document Type What is the format of the document? Is it a technical report, a white paper, a news article, an e-service application, a FAQ, a product specification?
- Source Who created this document? Which department was responsible for its creation?
- Intended Audience For whom is this document intended or appropriate? Which segments of our customers or employees may or may not be interested?
- Geography Is this document only applicable to people in specific regions, countries, or locations?
- Price Is there a price associated with this document or the products it describes?
You can undoubtedly come up with many more ways to describe a document. What's important is that the bottom-up approach leads you toward the identification of many facets, and eventually the creation of multiple taxonomies.
To bring this discussion of faceted classification down to earth, it may be helpful to consider the more established world of databases. All we're doing here is applying the principles of relational database design and the notion of fields within a database to the muddier world of Web sites and intranets. Facets are fields. And, in most contexts, you'll want to define multiple fields, rather than lumping apples, oranges, and papayas into one big container.
Controlled Vocabularies
Where facets are fields, controlled vocabularies are acceptable values. For each concept within a facet, you'll need to define a preferred term (i.e., acceptable value) and one or more variant or equivalent terms. This will enable your system to manage synonyms, homonyms, misspellings, abbreviations and acronyms, and other ambiguities of language and categorization.
Some of these facets will be flat lists. For example, you may have a single flat list of ten to twenty logical document types. Others, such as geography, may be hierarchical taxonomies, specifying office locations within cities within states within countries within continents.
As you're developing these controlled vocabularies, it's critical to work on the details with a view of the whole. Design of a topical taxonomy, for example, should be influenced by the existence (or lack thereof) of a product taxonomy or a geographic taxonomy. This awareness will make all the difference between focused, complementary vocabularies and ones that are confused and overlapping.
