When you are searching Entrez, have you ever gone to another Web site or to your library’s bookshelves in order to obtain additional information about what you retrieved? For example, suppose that you are browsing the Entrez Taxonomy database and you come across an entry for Ginkgo biloba. You may have heard of this plant many times, but what exactly does it look like? Or maybe you are looking at a Drosophila melanogaster sequence within the Entrez Nucleotide database. Wouldn’t it be convenient if you could quickly see the corresponding record in a different biological database, such as FlyBase?

You no longer have far to go to retrieve outside information. Just follow the LinkOut hyperlinks located within individual Entrez records and you will be able to explore additional information from sources located around the world.

LinkOut is a feature of Entrez that is designed to provide users with hyperlinks from records in Entrez databases to a wide variety of relevant Web-accessible online resources, including full-text publications, biological databases, research tools, and more. The goal of LinkOut is to facilitate access to relevant online resources beyond the Entrez system in order to extend, clarify, or supplement information found in the Entrez databases.



LinkOut resources for Ginkgo biloba, with menu showing Entrez display options


Let’s take a look at the Ginkgo biloba example once again. To get to the record, enter Ginkgo biloba in the Entrez Taxonomy search box. LinkOut hyperlinks (see Figure) can take you to the Gymnosperm Database where you will find a concise description of this tree, furnished with pictures of the tree, its bark, fruits, and foliage. Other links from this Entrez record tell you even more. The link for Canadian Poisonous Plants Information System provides information relating to the toxic effects of the tree. The New Crops Resource Online Program and HerbMed hyperlinks offer information on Ginkgo biloba’s value as a medicinal herb.

Links to external resources are listed in the LinkOut display of an Entrez record. Users can access the LinkOut display by selecting LinkOut from the drop-down menu located next to the Display button. Clicking on the Display button will then show the various LinkOut resources for a given record. From the PubMed database, these external LinkOut resources can also be accessed through an icon from the Abstract and Citation formats. Users can customize LinkOut display formats through LinkOut Preferences located in the Cubby.

A tutorial on using LinkOut is available from the LinkOut home page at www.ncbi.nlm.nih.gov/entrez/linkout.

If you know of online resources that might be valuable to Entrez users, please contact NCBI or the database provider. We are actively seeking new participants. Generally, high quality, easy to use resources that are directly relevant to particular Entrez records are good candidates. See the LinkOut home page for detailed information on how to provide links for Entrez databases.

Please send your questions or comments to linkout@ncbi.nlm nih.gov. —KK, BT