n general, the National Library of Medicine (NLM) performs two types of data correction or enhancement for MEDLINE citations:

1. Individual maintenance where a single citation is edited to fix an error specific to that citation (such as a misspelled author name or abstract word) or to enhance a specific citation (such as adding commentary elements), and
2. Class maintenance where multiple citations that share the same condition are all changed at once. Typically this global type of maintenance has been reserved for the annual year-end cycle in the past.

One benefit of the recent reinvention of the data creation and maintenance system for MEDLINE is the ability to do global or class maintenance throughout the year. While certain global changes will still be held for the annual year-end cycle for now (such as the Medical Subject Heading (MeSH^®) changes), other global changes will be done periodically during the year, improving the MEDLINE data in a more timely manner for both PubMed^® and NLM licensees. Examples of global changes that NLM will perform during the year include:

• Supplementary Concept Record names of substance or registry numbers
• Journal title abbreviations or ISSNs
• Clean up of data to improve consistency such as providing additional PubMed Unique Identifiers (PMIDs) for the Comments/Corrections family of fields so that links are possible in PubMed
• Enhancement of data to assist in retrieval such as adding certain access points to older citations as when a MeSH heading is added to citations indexed prior to the introduction of the heading to MeSH

Certain global edits will simply be done and not announced. When these global edits are important for the searcher to know, they will be announced in this publication.

Here are two MeSH-related MEDLINE global edits that have been done since the 2001 annual year-end cycle was completed:

1. The old MeSH heading "Chromosome Abnormalities" was class maintained to "Chromosome Aberrations" as part of year-end processing. Since then, the new 2002 heading "Chromosome Disorders" has also been added to those citations.
2. To all citations with any heading in the Muscles [A02.633] and [A10.690] trees also having the subheading "growth & development," NLM has also added the new 2002 heading "Muscle Development."

These two maintenance actions were applied only to citations indexed through the 2001 indexing year (i.e., those with a Date Completed (DCOM field in MEDLINE format) earlier than November 2, 2001).

By Lou Knecht
Bibliographic Services Division

Knecht L. MEDLINE^® Maintenance. NLM Tech Bull. 2002 Jan-Feb;(324):e8.