You should be familiar with the basic concepts of these specifications:
ebXML Registry Information Model Version 3.0
ebXML Registry Services and Protocols Version 3.0
You can find the latest public versions of these specifications by going to the OASIS web site and following the links to ebXML RIM V3.0 and ebXML RS V3.0.
Service Registry is available as part of the Java Web Services Developer Pack (http://java.sun.com/webservices/jwsdp/) or as a component of Sun Java Enterprise System, a software infrastructure that supports enterprise applications distributed across a network or Internet environment. If you purchased Service Registry as a component of Java Enterprise System, you should be familiar with the system documentation at http://docs.sun.com/coll/1286.1.