The UMLS or Unified Medical Language System is a collection of many resources it contains tools, a semantic network and a specialist lexicon. It is also a collection of many resources. These resources all have their own license and copyright. Effectively much of the UMLS can be used for many purposes because the particular license allows it. In the same way, there is much of the UMLS that can only be used when the copyright holder gives permission.
In OmegaWiki, we have our first Authoritative Database online. It is the UMLS and we are proud of it. Now as the UMLS is this collection of connected resources, we present it in the same way. There is one UMLS as an Authoritative Database and it has collections that are the parts that make up the UMLS as we have it. The important thing of the UMLS is that it did make the connection between the different databases and we do use their system to connect.
What makes the inclusion of the UMLS so special is that we have the cooperation of the NLM. It is what makes this such an exciting experiment.