Figure 1. GEO schema and example. (A) The entity-relationship diagram for the GEO database. (B) An actual example of three samples referencing one platformand contained in a single series.

At the time of writing, it is possible to retrieve complete platforms, samples and series submissions by accession number only. Extensive indexing and linking on the data in GEO has been performed and is queriable through a new Entrez database, named Entrez ProbeSet. The web interface to this database utilizes the same indexing and linking engine familiar through other popular NCBI resources such as PubMed and GenBank. As with any other Entrez database, a simple Boolean phrase may be entered and restricted to any number of supported attribute fields. Matches are linked to the full GEO entry as well as to other Entrez databases—currently Nucleotide, Taxonomy and PubMed—as well as related Entrez Probe Set entries. Entrez Probe Set is accessible through the Entrez web site (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=geo) as one of the drop-down menus used toselect the Entrez database to be queried.