The basic unit (defined by a unique identifier, or UID, in Entrez parlance) in Entrez ProbeSet is the GEO sample, fused with its affiliated platform and series information. The indexing process iterates through all platforms in the GEO database, extracting metadata and the data table and fishing for any sequence-based identifiers such as GenBank Accession, ORFs, Clone IDs, or SAGE tags. Each sample belonging to that platform is in turn assigned a new UID and indexed with the above platform information plus any related series metadata (Table 2).
GenBank Accessions, PubMed references, and taxonomy information are also linked to the appropriate Entrez databases for cross-reference and appear in the Links section of the display. Neighbors (related intra-Entrez database links) are generated for UIDs sharing the same GEO platform or series.
From: Chapter 6, The Gene Expression Omnibus (GEO): A Gene Expression and Hybridization Repository
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