I’ve given a rule-of-thumb of 3-8 facets to create in a faceted taxonomy, but it’s not that simple, and there are various factors to
consider. Creating facets is an assignment in the online taxonomy course I
teach, and a student recently submitted good set of facets with sample terms,
but there were 12 of them. So, why might that be too many facets?
Consider the users.
Are the users internal trained employees who deal with
content, most or all of the employees of an organization, external but repeat
users such as partners or researchers, or the general public? Internal employees,
especially those who are content managers or digital asset managers, who receive
some training to become familiar with the facets, should be able to handle any
number of facets. It is their job to classify and/or retrieve content by their
facets, so they should have the time and inclination to go through a long list
of facets. A broader cross-section of employees or external repeat users may
have access to documentation but not read it, will likely not be trained, and are
often more rushed when they deal with content, so a shorter list of facets
would be more suitable. Finally, the general public is likely to use only
facets that are easy to understand and fit into the window display (not
requiring scrolling), so a relatively short list of facets is recommended for
them.
Consider the content.
In addition to considering the shared attributes of
the content, as you cannot create more facets than conceptually exist for the
content, you need to consider the volume of the content. A relatively small
collection of content items or assets does not need as many facets as filters
than a larger collection of content does. If users select a term from each
facet, they should not be getting zero results or just one or two items too
often. Remember, the main use of facets is to filter and limit results down to
a list that can then be easily browsed. If the user retrieves only one or two
results, however, they will likely consider the search as too narrow and try
again to broaden it.
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| Microbial Life Educational Resources facets are just enough to fill the length of a computer monitor display. |
Consider the user interface.
Sometime the taxonomy has influence over the user
interface design, such as when it’s an internally designed research portal, but
often content management system do not offer much flexibility in how facets are
displayed. The first thing to consider is how many facets will be displayed by
default in the initial screen view (without scrolling) in the most commonly
used devices. If facets can be collapsed to show only the facet names and not
any values/terms within them, then a greater number of facets can more easily
be included. Hiding the values, however, might not be desired, since the
display of sample values makes it clear to the user what the facets are for.
Consider what constitutes a facet or filter.
What may be considered a “faceted taxonomy” is only a subset of all the possible metadata properties of
the content. Some of the other, default non-taxonomy metadata (such as date,
creator, file name or title, or file type) may also be desired as end-user
filters alongside the taxonomy facets, which then further increases the number
of filters or refinements displayed to the user, who sees no difference between
taxonomy facts and non-taxonomy filters.
There is no strict definition of a “taxonomy facet.” I
would say it is a facet whose values or terms must be created by a person, such
as a taxonomist or metadata architect, rather than those that are system-generated.
In addition, taxonomy terms are those that must be tagged to the content, rather than already being a part of content. For
example, if File Format is based on the file extension, then it is already part
of the content and need not be “tagged,” so it’s not a taxonomy facet by my definition.
A faceted taxonomy is more, though, than a single
facet of topics alongside other non-taxonomy metadata. The idea behind creating
a faceted taxonomy is to split up what could be a large hierarchical taxonomy
into different aspects. For example,
instead of having a term Business service agreements that is in a hierarchy narrower
to both Vendor contracts and Business services, you could have just the term
Vendor contracts in the Document Type facet and Business services in the
Business Type facet, and the combination of the terms from each facet will
suffice.
Faceted taxonomies, more so than hierarchical taxonomies
or thesauri, need to consider the factors of users, content, and user interface
when it comes to their design.
