TBD (Take from https://blog.g-vo.org/adql-tricks-at-mpia/)
For many interesting discovery problems, a simple parameter-based interface as in registry.search just isn’t powerful enough. Fortunately, if you know TAP and the (admittedly somewhat complicated) relational mapping of the Registry data model, you can get almost arbitrarily fancy. This is called RegTAP and is available from reg.g-vo.org (and a few other TAP services). There, you can query roughly a dozen tables that contain the service metadata. To learn more, inspect the metadata of the tables in the rr schema (they are designed to be joined using NATURAL JOINs) if you want to know more, and if you’re still not satisfied, there’s more explanations and examples in the underlying standard.
Here, we combine the tables of interfaces (things a client can talk to), capabilities (ways of using a services, in this case: TAP), and details (various “minor” properties of resources; in this case: implementation of a data model).
This may look a bit complex, but it’s fairly stereotypic. If you have somewhat more advanced data discovery problems and want to come up with queries of this sort yourself, you may want to read 2015A&C....10...88D.