UDDI 3.0 is a version of UDDI that expanded on UDDI 2.0. The primary enhancements dealt with registry-to-registry interaction. This included the interaction between both public and private registries.

From the UDDI Features Document:
“With a vast array of enhancements – including multi-registry topologies, increased security features, improved WSDL support, a new subscription API and core information model advances – the Version 3 specification offers clients and implementers a comprehensive and complete blueprint of a description and discovery foundation for a diverse set of Web services architectures.”

Here is the UDDI 3.0 Specification.