Keywords are words and phrases used to name an article’s or section’s key concepts for
search and retrieval purposes. Typically an author, publisher, or indexing service will assign a small
number of key terms to expand lookup beyond full text, to point up the most important topics
described in an article, or to map an article to a taxonomy. Indexers assigning keywords can make
sure that someone searching for “this topic” will find this article or section, even
if the exact words are not present in the text. Thus keywords may be key words taken from the text, from an outside
vocabulary or taxonomy, or selected by authors, indexers, or publishers.
In this Tag Set, keywords come in sets (
<kwd-group>), each of which may come from a particular source or ontology (such as
“
author-created” or the
“
MeSH Subject Headings”). The sets are
named using the
Keyword Authority attribute.
Here are some sample tagged keywords that a contributor chose as best describing an
article:
<kwd-group kwd-group-type="author-created">
<kwd>acid precipitation</kwd>
<kwd>acid rainfall</kwd>
<kwd>smelting region</kwd>
<kwd>Aluminum residues</kwd>
<kwd>Sulphur dioxide</kwd>
<kwd>Copper-nickel smelters</kwd>
</kwd-group>
Earlier versions of this Tag Set allowed for multiple sets of keywords, but
the individual keywords in the set had no structure; they were just text, words, and
phrases — possibly with face markup, superscripts, and subscripts (such
as “<kwd>XML</kwd>”,
“<kwd>H<sub>2</sub>O</kwd>”, and
“<kwd>blood-brain barrier</kwd>”). The current NISO JATS
accommodates more elaborate keyword structures as described below.
Keywords can possess an internal structure of their own; for example, a keyword may
include both a textual phrase and its corresponding code (“863 Icelandic
sagas”). Many styles of such compound keywords can be handled in this Tag Set
with the
<compound-kwd> element, which is
modeled as a series of repeatable parts (
<compound-kwd-part>). These parts can differentiate a text/code pair, divide a coded
keyword into multiple code segments, describe a hierarchy, and name a variety of other
compound structures. The
@content-type
attribute on the
<compound-kwd-part>
element is used to name each part, describe the role it plays, or otherwise define how
each part functions within the keyword as a whole.
The simplest case of a compound keyword is a keyword that includes both a textual
phrase and its corresponding code, for example, “863 Icelandic sagas”.
Both the code and the text can be tagged as keywords parts (
<compound-kwd-part>) inside the element
<compound-kwd>, with the
@content-type attribute used to name the role or
type of each part:
<kwd-group kwd-group-type="ISO-463">
<compound-kwd>
<compound-kwd-part
content-type="ISO-463-code">863</compound-kwd-part>
<compound-kwd-part
content-type="ISO-463-text">Icelandic sagas</compound-kwd-part>
</compound-kwd>
...
</kwd-group>
Compound keywords can also be used to handle keywords that hold an abbreviation
and its expansion. Both the abbreviation and the expansion are tagged as
<compound-kwd-part> in a single
<compound-kwd>. The
@kwd-group-type attribute on
<kwd-group>, which is sometimes used to name the
source or the descriptor for the keywords, can be used instead to name the type of
information, such as “abbreviations”. For example:
<kwd-group kwd-group-type="abbreviations">
<compound-kwd>
<compound-kwd-part content-type="abbrev">WT</compound-kwd-part>
<compound-kwd-part content-type="expansion">WildType</compound-kwd-part>
</compound-kwd>
<compound-kwd>
<compound-kwd-part content-type="abbrev">CFU</compound-kwd-part>
<compound-kwd-part content-type="expansion">Colony-forming unit</compound-kwd-part>
</compound-kwd>
</kwd-group>
Some publishers assign hierarchical topics to articles. For example, a publisher
might tag selected topics (“Blood–brain barrier”), nested inside themes
(“Cellular and Molecular Biology”), grouped into larger units like
“Neuroscience”, and grouped into still larger units such as
“Biological Sciences”, forming the following hierarchy:
Biological Sciences
Neuroscience
Cellular and Molecular Biology
Blood–brain barrierThis kind of structure places an article in context or sorts articles into
categories. This is commonly seen in Tables of Contents, where all the Neuroscience
articles are grouped together and all the Biochemistry articles are grouped, etc.
Since keywords are intended to aid in searching and retrieval of articles
rather than establishing an article’s context, best practice is to tag this
topic structure as subject groups:
<article-categories>
<subj-group subj-group-type="keywords">
<subject>Biological Sciences</subject>
<subj-group subj-group-type="keywords">
<subject>Neuroscience</subject>
<subj-group subj-group-type="keywords">
<subject>Cellular and Molecular Biology</subject>
<subj-group subj-group-type="keywords">
<subject>Blood–brain barrier</subject>
</subj-group>
</subj-group>
</subj-group>
</subj-group>
</article-categories>
But Hierarchical (nested) keywords structures are also possible. These, while still rare, are
becoming more common as taxonomies are used to tag keywords for articles. Each
<nested-kwd> contains a single keyword and any levels of nesting under that
keyword. Since nested keywords are recursive, these lower levels are inside an inner
<nested-kwd>. The same example is used below to show how nested keywords work.
<kwd-group kwd-group-type="author" xml:lang="en">
<nested-kwd>
<kwd>Biological Sciences</kwd>
<nested-kwd>
<kwd>Neuroscience</kwd>
<nested-kwd>
<kwd>Cellular and Molecular Biology</kwd>
<nested-kwd>
<kwd>Blood–brain barrier</kwd>
</nested-kwd>
</nested-kwd>
</nested-kwd>
</nested-kwd>
</kwd-group>