Database Size and Shape (MeSH Thesaurus) – Ovid MEDLINE

Background

Drawing again on the idea of the ‘size and shape’ of databases, this Focused Search provides an introduction to the structure and system of the MeSH thesaurus. The MeSH thesaurus is a controlled vocabulary, based upon medical subject headings. It has been created and is maintained by the National Library of Medicine (NLM) in the USA. The MeSH thesaurus is a domain specific knowledge base curated by humans, that aids both document classification as well as discoverability and retrieval.

MeSH Structure and System

Ovid MEDLINE is Ovid’s rendering of the PubMed database, it too created and maintained by NLM. The content of this kind of bibliographic database consists, for the most part, of records of documents that have been indexed using a controlled vocabulary. A controlled vocabulary is a hierarchical term classification system where terms, representing a thing or concept, can be located within the controlled vocabulary system, along with its broader and narrower terms. For an informative optical rendering of this enter the search term ‘migraine disorders’ into the MeSH database search box as shown below.

https://www.ncbi.nlm.nih.gov/mesh/?term=migraine+disorders

The returned screen provides detailed background information on the target term. Amid the detail is also an indication of where the target term, here ‘migraine disorders’ appears in the MeSH term hierarchy. In the enhanced diagram below the blue bordered terms represent the broader terms associated with ‘migraine disorders’. By contrast the thinner green bordered expressions are its narrower terms. Which is to say that the idea or concept represented by the MeSH term ‘migraine disorders’ can itself be further broken down into finer ideas or sub-concepts, specifically ‘Alice in Wonderland Syndrome’, ‘Migraine with Aura’, ‘Migraine without Aura’ and ‘Ophthalmoplegic Migraine’.

Understanding the MeSH term constellation for your target terms or terms, and being able to navigate through the thesaurus hierarchy effectively, will greatly assist you in the systematic construction of high quality search queries.

In PubMed the MeSH database is a stand-alone, albeit connected, knowledge resource. By contrast the MeSH thesaurus is fully integrated into the Ovid MEDLINE search experience. MeSH terms can be easily located in the thesaurus hierarchy and narrower terms selected (as well as deselected) either as a group or individually as you decide. When you choose to include all of the MeSH terms narrower terms, you are said to have “exploded” the term. The Explode function and a related function, called Focus will be covered in the next Focused Search, Knowledge Discovery with MeSH (Explode & Focus) – Ovid MEDLINE.

Practice Suggestions:

1. Go to the Advanced Search. Check that the option Map term to Subject Heading is activated, that is ticked, and enter as a Keyword the expression migraine disorders. Looking at the screen that is subsequently displayed, list at least 4 options you could act on from there.
2. Go again to the Advanced Search. Deselect the option Map term to Subject Heading and as before enter as a Keyword the expression migraine disorders. Looking at the screen that is subsequently displayed, what kind of search has Ovid executed? Where do you think Ovid has searched for your term?  
3. In the Focused Search used in this example, how can you verify that the results in line #2 are included in the .mp search, run in line #3?

 

Search Stategy

Copy Strategy Launch Search

Reviewers

Primary: Michael Fanning

Secondary: Charlotte Viken

Review Date: 2024-10-27

Expiry Date: 2025-10-27

Original search produced by:

Ovid Training Team

References:

OvidGO! / Skills Videos
What is Ovid MEDLINE
Ovid MEDLINE segments explained
How to customize Ovid MEDLINE segments
How is indexing done in MEDLINE
Subject heading searching

Citation:

OvidGO! Portal. Focused Searches: Database Size and Shape (MeSH Thesaurus) – Ovid MEDLINE [Internet]. London (UK): Ovid Training Team (Editors); 2024 [updated 25 October 2024; cited 30 October 2024]. Available from: https://tools.ovid.com/ovidgo/searches/view.php?id=57