One of the benefits of a taxonomy is that there are
relationships between the terms to support navigating to find the most suitable
term. This could be the multi-level hierarchical browsing from broader terms
down to more specific narrower terms. In a strict definition of a taxonomy, the
only required type of relationship between terms is hierarchical. But sometimes
it may be desirable to have relationships other than hierarchical.
ISO and ANSI/NISO standards for controlled vocabularies are
very explicit on the criteria for hierarchical relationships between terms. The
narrower term must be a specific type of, an instance of, or an integral part
of its broader term, and it must be so in all circumstances, not just
sometimes. If a pair terms seem as if they should be related, but their
relationship does not meet the criteria for a hierarchical relationship, then
they could have an associative
relationship instead, which is also known as “related term” or abbreviated as
RT. Examples include Schools as related to School busses, Computers related to
Operating systems, and Business development related to Marketing
Those familiar with controlled vocabularies, know that the
RT relationship is a standard feature of a thesaurus, whereas it is not common
in taxonomies. However, the distinction between a taxonomy and a thesaurus can
be blurred, and the kind of controlled vocabulary that is designed and
implemented can have features of both, serving the needs of the users and the
nature of the content and indexing. Therefore, taxonomists should have a good
understanding of the associative relationship, in case the need arises and the
system supports it.
The creation of an RT relationship is more subjective than
the creation of hierarchical relationships. Even the standard ANSI/NISO
Z39.19-2005 (r2010), in section 8.4 Associative Relationships admits "The
associative relationship is the most difficult to define." The standard
states that the relationship is created "on the grounds that it may
suggest additional terms for use in indexing or retrieval." The fact that
the relationship may be created but is not required in many circumstances
leaves it up to the best judgment of the taxonomist.
The only required circumstance for the RT relationship (in a
thesaurus or taxonomy that has associative relationships) is between two terms
that share the same broader term and they
have some overlapping meaning. Examples include Boats and Ships (sharing the
broader term Vessels), or Tablets and eReaders (sharing the broader term Mobile
devices), or Coats and Jackets (sharing the broader term Outerwear). But there
would not be a related-term relationship between Coats and Mittens, even though
they are both narrower terms of Outerwear, because they don’t have overlapping
meaning.
More often, however, the RT relationship is created between
terms with different broader terms or even from different hierarchies entirely.
The ANSI/NISO Z39.19 standard provides guidance on this only to the extent of
when the relationship may be created.
Whether creating the relationship is a good idea or not is up to the
taxonomist’s discretion and ultimately depends on what the taxonomist thinks
would be helpful to most users.
Following are examples of possible RT relationships between pairs of
terms:
Baseball RT Baseball
players
Ventilation RT Fans
Bacterial infections
RT Antibiotics
Appliance repair RT
Appliances
Plastics RT
Elasticity
Timber RT Wood
products
Psychology RT
Psychologists
Literature RT Books
There are different users of a taxonomy/thesaurus with
different goals. Depending on what they are looking for, some users would
welcome the guidance of a certain RT relationship, pointing them to a related
term they had not considered but find helpful (such as E-commerce RT Online
shopping); whereas other users are not interested in the related term and may
find extra RT relationships getting in their way. The goal is to provide RT
relationships that are probably relevant and helpful to the majority of users
or “the average user,” while realistically not expecting to serve all users.
The following are examples of RT relationships that are not likely to
be helpful to most users and thus better not be created:
Newspapers RT
Advertising
Germany RT World War
II
Athletics RT Doping
A good way to become more familiar with best practices for
creating RT relationships is to browse published thesauri with these
relationships. Thesauri that are available publicly to browse on the web
include the ERIC (Educational Resources Information Center) Thesaurus, MeSH
(Medical Subject Headings), UNESCO thesaurus, and the NASA thesaurus. These and
others can be found on the American Society for Indexing’s website page OnlineThesauri and Authority Files. Note that related terms might be indicated as RT, Related concepts, or See also
links.
Creating associative relationships is part of the creative
work of taxonomists, but taxonomists must remember that serving the user is the
primary goal.