It’s quite common in a faceted taxonomy to have a Document/Content Type facet (I’ll call DocType here), whose terms define what a content item “is,” (a report, a blogpost, a form, a contract, a letter, a policy, etc.) and also a Topic or Subject facet, whose terms describe what a content item is “about” (legal compliance, training, new business, insurance, company information, etc.) While usually it’s pretty clear-cut what belongs in the DocType facet and what belongs in the Topic facet, occasionally there are some ambiguous concepts, so asking the questions “what is it?” versus “what is it about?” helps in making the distinction.
Often the taxonomist can resolve ambiguity by editing the term so that a one-word generic document type is appended to a descriptive word. For example “Marketing” by itself is a Topic, but “Marketing Material” is a DocType. This kind of decision is reached only after looking at the set of documents and determining whether there is a significant number of them that are really marketing materials versus a significant number of them that are really about marketing (and there could be both). You then have to decide how far to go with this. You could force otherwise topical concepts into DocTypes by adding the word “Document” to the end of many terms. For example, “Compliance” becomes “Compliance Document”, and Client Management” becomes “Client Management Document.” Depending on your overall content set and taxonomy design, this may or may not be acceptable practice.
Another complicating issue that may come up in designing such a faceted taxonomy is what to do if certain Topics only occur in certain types of documents. This is not unusual. While DocTypes such as Report, Evaluation, Meeting Minutes, Memo, Article, Review, etc., are rather generic and could all be associated with any number of the same shared set of Topics, other DocTypes that a customized for a specific content set are more limited in their application. For example, Topics for different types of approval to be used only with a DocType of “Approval Letter,” or Topics for types of product information to be used only with a DocType of “Product Information Sheet.”
There are two ways to handle this issue:
1. Create rules permitting certain Topics available as options only when certain DocTypes are assigned
This requires that DocType be assigned (tagged, indexed, matched, etc.) to a content item first, before the Topic is assigned. This can be seen as: the Topic is dependent on the DocType, or DocTypes terms drive the Topics, or the DocType takes precedence over the Topic. This is feasible with these facets, since a content item can be assigned only on DocType (in contrast with the possibility of getting assigned more than one Topic). What gets complicated, though, if there are additional rules between other facets, with the terms in one facet driving the availability of terms in other facets, such as File Type, Source, Department, etc.
2. Merge the DocType and Topic facet into a single facet
This may seem extreme, but it could be practical, especially if it’s easier for the end-user. It works if the there are not so many Topic terms, such as not many more than the total number of DocType terms, the majority of them are applicable to a single DocType term, and a user interface can be designed that supports an expandable/collapsible hierarchy, so a user clicks on a DocType and the applicable Topics underneath it display. Traditionally taxonomies are hierarchical after all. If a Topic term is valid for more than on DocType, then a valid polyhierarchy results. There could still be a distinct facet for File Type/Format (such as HTML, text, image, PDF, etc.), for which there would be no ambiguity, in contrast to the occasional ambiguity between DocTypes and Topics.