Page 136 - DLIS405_INFORMATION_STORAGE_AND_RETRIEVAL

Unit 13: Subject Headings

Descriptor Hierarchy Notes

The descriptors or subject headings are arranged in a hierarchy. A given descriptor may appear at
several places in the hierarchical tree. The tree locations carry systematic labels known as tree numbers,
and consequently one descriptor can carry several tree numbers. For example, the descriptor “Digestive
System Neoplasms” has the tree numbers C06.301 and C04.588.274; C stands for Diseases, C06 for
Digestive System Diseases and C06.301 for Digestive System Neoplasms; C04 for Neoplasms, C04.588
for Neoplasms By Site, and C04.588.274 also for Digestive System Neoplasms. The tree numbers of a
given descriptor are subject to change as MeSH is updated. Every descriptor also carries a unique
alphanumerical ID that will not change.

Descriptions

Most subject headings come with a short description or definition. The explanatory text is written by
the MeSH team based on their standard sources if not otherwise stated. References are mostly
encyclopaedias and standard textbooks of the subject areas. References for specific statements in the
descriptions are not given, instead readers are referred to the bibliography.

Qualifiers

In addition to the descriptor hierarchy, MeSH contains a small number of standard qualifiers (also
known as subheadings), which can be added to descriptors to narrow down the topic. For example,
“Measles” is a descriptor and “epidemiology” is a qualifier; “Measles/epidemiology” describes the
subheading of epidemiological articles about Measles. The “epidemiology” qualifier can be added to
all other disease descriptors. Not all descriptor/qualifier combinations are allowed since some of
them may be meaningless. In all there are 83 different qualifiers.

Supplements

In addition to the descriptors, MeSH also contains some 139,000 Supplementary Concept Records.
These do not belong to the controlled vocabulary as such and are not used for indexing MEDLINE
articles; instead they enlarge the thesaurus and contain links to the closest fitting descriptor to be
used in a MEDLINE search. Many of these records describe chemical substances.

Use in Medline/PubMed

In MEDLINE/PubMed, every journal article is indexed with some 10-15 headings and subheadings,
with some of them designated as major and marked with an asterisk. When performing a MEDLINE
search via PubMed, entry terms are automatically translated into (= ‘mapped to) the corresponding
descriptors with a good degree of reliability; it is recommended to check the Details tab in PubMed to
see how a search formulation was ‘translated’. By default a search will include all the descriptors that
are located below the given one in the hierarchy.
The Medical Subject Headings (or MeSH for short) is designed to help you focus your search, and to
avoid ambiguous terms or synonyms, i.e. where one words can mean many different things, or
where different words are used for the same topic.

Medical Subject Headings (MeSH) Indexing Tips

Medical Subject Headings (MeSH) is a list (thesaurus) of keywords or descriptors that describe articles
in Index Medicus and MEDLINE. Indexers scan an entire article and assign up to twenty MeSH terms
to each article. Terms are chosen to cover both the central aspects of an article (major headings) and
other significant information discussed (minor headings).
By using terms from the MeSH thesaurus, all articles on a given topic can be found regardless of the
terminology used by the authors.

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