Underlying and connecting the several databases within the Entrez system is an extensive network of links and precalculated similarity data that have been relatively inaccessible to users. In an effort to assist researchers in finding these links and using them to discover interesting relationships within the NCBI databases, NCBI is developing three types of ‘discovery components’ on Entrez web pages: sensors, which analyze search queries and display data potentially related to the query terms; database ‘ads’, which promote links to highly relevant data in a different database; and analysis tools, which provide further insight on the record being viewed. Examples of such components released so far include the citation and gene sensors in PubMed that, respectively, activate when citation elements or gene symbols appear in a query; the PubMed Central (PMC) and three-dimensional (3D) structure ads on PubMed abstract pages that provide links to free full-text articles or 3D structures reported by the paper; and BLAST and Primer-BLAST links provided on nucleotide sequence records. As part of this effort, the nucleotide and protein record pages were redesigned to highlight numerous links from sequences to related data including literature, Reference Sequences (RefSeqs), genes, gene homologs, transcript clusters, clones and conserved domains.
