NB! This is for advanced users. Most of the time you will do fine without much knowledge about the relevant thesaurus.
Almost all databases have their own (often hierarchical) system of subject terms to classify publications = thesaurus. These are added to the article by editors, and are independent of the actual language used by the author in the text. This means that if you search for a subject term that is present in the thesaurus, you will find publications about this subject regardless of what terms the authors have used.
Using the database's thesaurus can also be useful if you are interested in sorting out (or removing) publications within a certain subject. There are several ways you can make use of a thesaurus, it depends on the database. For example you can:
To properly use controlled vocabulary, you need to find out what system/thesaurus your favorite database is using. Here follows a few examples:
|BIOSIS Previews (A biological database within Web of Science)|
|Concept Codes: Life Science subject terms (click the link to read more)|
|Taxonomic Data: Taxonomic subject terms (click the link to read more)|
|MEDLINE (the database in PubMed)|
|MeSH-terms: Medical subject headings (click the link to read more)|
|Subject Terms: General subject headings (click the link to read more)|