Comparing biological concepts using keyword profiles. (a) A set of references from PubMed can be associated with a profile of keywords according to the Medical Subject Heading (MeSH) terms assigned to them. By extension, this can be done for any concept or database record with an associated set of PubMed references. (b) Entrez (human) genes, diseases (defined as MeSH terms) or chemicals (defined as MeSH terms) can be associated with bibliographic records in PubMed, and therefore can be defined by profiles based on any MeSH terms (middle). Conversely, it is possible to find the genes, chemicals and diseases associated with particular MeSH terms. Associations between concepts (genes and diseases, but also genes and chemicals, or diseases and chemicals) can be defined by comparing such profiles. This figure is partly taken, with permission, from the MeSHOPs website .