How to cite curated databases and how to make them citable

Curated scientific databases such as the IUPHAR database resemble conventional publications such as reference manuals in that they represent the work of a large number of people who both create and revise their contents. The difference is that curated databases have more internal structure and that they change more frequently. How should we cite all or parts of such a database? We use conventional citations primarily to identify the source material, but this is not their only use. They are distinguished from persistent object identifiers (or other "randomly" assigned digital keys) in their ability to provide some additional information, such as authorship or title that may be useful even before we look at the cited work