One infrequently discussed aspect the UDDI Business Registry (UBR) Version 2is the implementation of the UDDI Replication specification. It is a shame this gets such little attention, because replication is quite impressive. (Then again, when technology works, nobody pays attention...)
So what is UDDI Replication anyway? When two or more UDDI "nodes" are integrated into a UDDI "registry," the use of the UDDI Replication API allows the registry to be viewed as a single logical entity. A registry designed in this way supports uniform access to a complete set of registry data from any node within the registry. The goal of replication is to facilitate the establishment and maintenance of a single consistent shared set of registry data. Replication latency notwithstanding, all nodes in a registry should at all times contain common content.
In the UBR, replication between the three nodes (SAP, IBM and Microsoft) happens on an hourly basis. Each node polls the other nodes to get change records. The key to the replication topology working is the Originating Update Sequence Number (USN). By maintaining an ever increasing USN, what is known as the high water mark vector can be provided when changes are requested. What does this all mean? Nodes share out their changes so that other nodes are always up to date.
So why does replication rule? First off, the Replication API is entirely SOAP and XML-based and is a prime example of an interoperable Web service. The SAP and IBM implementations work great against Microsoft's .NET implementation. Second, the Replication API is validation of the interoperability between the different UDDI implementations, demonstrating the strength of the UDDI specification across multiple vendors. Third, the Replication API is an example of writing secure Web services. Not only do the SOAP messages use HTTPS, they also use X.509 v3 client certificates with every message.
I would encourage you to check out the replication behavior by saving data to one of the UBR nodes and watching it replicate across to the other two UBR nodes.
