National Library of Medicine has published information on the linkout program. LinkOut is a feature of Entrez that is designed to provide users with links from PubMed and other Entrez databases to a wide variety of relevant web-accessible online resources, including full-text publications, biological databases, consumer health information, research tools, and more. This is one of a number of efforts to tie medical information resoures together.
Another recent attempt to build unity in health information resources is HEAL. Health Education Assets Library (HEAL) was started with funding of the National Science Foundation and in collaboration with National Library of Medicine. It's a cool idea. Link medical education resources together. I create class materials .. share them through HEAL with you .. and you don't have to re-invent the wheel. They have defined a core set of decriptors. and they invision that we will all share information about the resources in XML. I think I'll work on making fpclassroom.org compliant with their site .. so that we can share data with them. XML and "web services" will change the way that most people think about websites. No kidding.