Taxonomies are versatile and may be used for various
purposes. Originally designed to support hierarchical browsing of topics linked
to content, they also may be implemented to support more accuracy in searching.
Most discussions of taxonomies have focused on browse and/or search, but
taxonomies may function in additional ways: enhancing filtering and sorting.
Filtering
Taxonomies structured into facets serve a combination of
search and browse, and thus serve what is often called “faceted search” or “faceted
browse” (as described in a previous blog post, Faceted Search vs. Faceted Browse). However,
it’s simpler, more accurate, and more helpful in understanding facets to
consider a faceted taxonomy as serving a distinct role from browsing or
searching, that of filtering.
Filtering is a common function which is not limited to use
with taxonomies. Filtering can be done by non-taxonomy attributes, such as keyword,
author, date, etc., if these are set up as metadata and implemented as filters.
We see filters in situations which lack taxonomies in options in the email
inbox or lists of documents in file management user interfaces. We also find
filters on documents in SharePoint libraries and other content/document
management systems, which may include taxonomies. In a user interface, the icon
for filtering is a funnel (where you can imagine that it is lined with a
cone-shaped filter paper).
Filters may be known by other names, such as
“Refinements”/“Refine by” or “Limit by.” These designations may be used
interchangeably, although they tend to be used different circumstances.
“Filtering” may be done on search results or on a complete set of records, such
as a list in a spreadsheet or table. “Refining” or “limiting,” on the other
hand, would usually be performed only on the results of an executed search, as
a further refinement or limiting factor on an initial set of search results
which turned out too large. “Refining,” furthermore, suggests a more careful
search process, so this name is more often used in research databases or other
repositories of articles and resources.
A relatively small faceted taxonomy comprising short lists
of terms for each facet/filter, from which the user can select from a displayed
list or drop-down, is both easy to use and, with proper tagging, can achieve
accurate retrieval results.
Sorting
Sorting is done on content in a spreadsheet or table, where
data on content items is in different columns, with sorting done by an
attribute of an individually selected column. Sorting could be by numeric
order, by alphabetic order, by date, or by the mere presence of a binary value.
Indeed, most sorting does not involve
taxonomies, but it can. If a column is
for “Topic” and items have been tagged with taxonomy terms, then the items can
be sorted by taxonomy term topic.
The function of sorting with taxonomy terms may not be quite
as common as filtering, since it is not done on search results but only on data
in a table or spreadsheet. However, in many situations content items are
presented this way: content in spreadsheets and databases, messages in an email
inbox, content items in SharePoint libraries and various kinds of content
management systems, and many other applications. Furthermore, it’s often
simpler to sort than to filter.
Sorting is nevertheless a function associated with
taxonomies, at least in the definition of taxonomy in the ISO standard for
controlled vocabularies. ISO 25964-2:2013 in section 3.83 defines taxonomy as a
“scheme of categories (3.5) and subcategories that can be used to sort and
otherwise organize items of knowledge or information.”
The following screenshot from SharePoint shows the
availability of both sorting (by clicking on the down-arrow next to a column
name, such as Topic), and filtering (by selecting Topics in the filter pane on
the right).
Summary
As taxonomies are versatile, the same taxonomy can be used
for multiple purposes: browsing, searching, filtering, and sorting. However, a
taxonomy design usually can be optimized for the user experience of only one or two
implementations. So, a taxonomy that
delivers a great user experience for hierarchical browsing, might not be best
suited for filtering or sorting, or vice versa. Filtering is more accommodating
for various taxonomies than is sorting, since it may not be necessary to
display the entire taxonomy in filters.
