Is a taxonomy the same as a classification scheme or system? Or, to put
it another way, is a classification system, such as the Dewey Decimal System, a
kind of taxonomy? Both of these kinds of knowledge organization systems have
the feature of arranging topical terms in a hierarchy of multiple levels, without having
related-term relationships or necessarily synonyms/nonpreferred terms, which
are features of thesauri. So, it appears as if the only difference is that
classification systems have some kind of notation or alphanumeric code
associated with each term, and taxonomies do not. The differences, however, are
greater than that.
Classification systems
The codes/notations in classifications are not merely shortcut
conveniences. They represent a way to divide up the area of knowledge into broad
classes, sub-classes, sub-sub-classes, etc. The codes/notations are not an
after-thought but are planned from the beginning of the design of a
classification system.
The classification is comprehensive; everything in the subject domain
is covered with a classification code + label. There is often not a lot of room
for expansion, except for a few unused sub-unit codes in each area for new
topics. The word classification means to put into a predefined class or
grouping. The approach to classification is thinking “where does this go?” (Digital
documents may go into more than one classification.)
Classification systems are not just used in libraries, but in corporate
settings too, such as for research literature or detailed manufacturing product
catalogs. The standard for defining knowledge organization systems for
interoperability on the web, the Simple Knowledge Organization System (SKOS), developed
by the World Wide Web Consortium (W3C), recognizes classifications systems, by
having a designated element for “notation.”
Taxonomies
A taxonomy is a kind of knowledge organization system that has its
terms hierarchically related to each other. The starting point in creating a
taxonomy might be a few top terms or facets, but then the focus of taxonomy
development is on the specific terms needed, rather than the division of a
domain into classes and subclasses, etc. What this means is that the terms do
not have to comprehensively cover the subject domain in an abstract manner.
Rather the terms have to “cover” the topics appearing in the body of content to
be tagged with the taxonomy.
The taxonomy is used for tagging or indexing, not for classification or
cataloging. So, rather than thinking where (into what class) does this document
go, the question is, what is/are the main topic(s) of this document. The topics
might not fall into neat balanced hierarchies. For example, an intranet
taxonomy might have a term for Temporary employees, because there are some
human resources policies dealing with this topic specifically, but have no term
for Full-time employees, since that is the default, and the term would not be
useful (and likely inconsistently tagged).
Different mindsets
Lumpers and splitters are historically two opposing viewpoints in
categorization and classification: whether you "lump" items into
large categories, focusing on the similarities, or "split" items into
more smaller categories, focusing on the differences. Of course, there is often
a combination of both approaches, but it is my feeling that the design of
modern taxonomies tends to involve more lumping, whereas the design of classification
systems has involved more splitting.
One of the challenges of working with subject matter experts (SMEs) in
building a taxonomy is that SMEs, as experts in their domain, may tend to think
of how to classify their domain, and propose a taxonomy that resembles a
classification system, even if it lacks the codes/notations. So, it’s very
important to provide precise guidelines to SMEs contributing to a taxonomy, explaining
that the terms are intended for tagging common topics that appear in the
content and are for limiting/filtering search results, and that full classification
is not necessary.
Students of library science may also tend to think of classification systems
as serving for taxonomies. They learn about classification systems when they
study cataloging, and subject cataloging is also about where the book or other
library material belongs (often literally, on the shelf). So, even librarians
need training on taxonomies and the taxonomy mindset if they want to become
taxonomists. I will be giving a taxonomy workshop at the Computers in Libraries conference in March, so I will be sharing these ideas with those who attend.
Classification systems often have Not Otherwise Specified and Not Elsewhere Classified terms, reflecting a lack of detail in the item being classified or the classification system, respectively. Some classification systems do leverage synonyms as entry terms.
ReplyDeleteAh, yes, those "not elsewhere classified" classifications that are not particularly useful to the users.
DeleteCan anyone classify "Not Otherwise Specified" and "Not Elsewhere Classified" in relation to each other? What system is the commenters referring to? Otherwise and Elsewhere are different elements of vocabulary.
ReplyDeleteExcellent article
ReplyDeleteGood article...
ReplyDeleteI was never clear on the differences--thank you for explaining!
ReplyDeleteI've now created a video based on this blog post:
ReplyDeletehttps://www.youtube.com/watch?v=2FFhiDs4LyA&feature=youtu.be