Integrated Access Across Databases (Hard Links)

• sometimes records in one Entrez database have associated records in other Entrez databases. For example, a PubMed record that discusses the sequence of a gene might have corresponding records in the Nucleotide and Protein databases. Regardless of which one of these databases you start your search in, you can easily traverse to the associated records in the other databases by using the "Links" menu.



• how links are made


• hard links:  one-to-one associations


• direct cross-reference
  (e.g., If a nucleotide record contains a protein translation for the CDS in the Feature field, it will link only to the Entrez Protein record that was created directly from that translation. If a nucleotide record cites a specific set of PubMed/MEDLINE IDs in the References field, it will link only to those PubMed/MEDLINE records, not to all records on that topic.)


• other type of direct association
  (e.g., links between Entrez Nucleotide and UniSTS records are made by comparing the two sets of data against each other using e-PCR -- if a primer pair in a UniSTS record is found to exist in a nucleotide sequence, then a link is made between those records.)


• what they link to, and what they do not link to

Demo: from the sample RefSeq record: NM_000249, follow Protein, Pubmed, and OMIM links as examples. Though the Protein database contains a number of records for the human MLH1 protein product, Entrez will only pull up the single protein record that was extracted directly from the CDS translation in NM_000249. Similarly, there are many PubMed records which discuss the human MLH1 gene, but when you follow the Links menu from NM_000249 to PubMed, you will only retrieve the PubMed records that are cited in the nucleotide sequence record. Finally, the OMIM records you retrieve will be those which cite at least one reference that is also in NM_000249. In any one of those databases, you could easily pull up additional, relevant records by following the link for "related" records (which you will do on the next slide...)