UDDI (Universal Description, Discovery and Integration) is a specification that describes a standard for publishing and discovering web services on the Internet. It’s essentially a repository with a rigid data structure that describes companies and the web services that they provide. UDDI is not as fundamental to web services and XML, SOAP, and WSDL, but it is considered a basic constituent of web services in J2EE.

The analogy normally used to describe UDDI is that it provides electronic White, Yellow, and Green pages for companies and their web services. You can look up companies by name or identifier (White pages) or by business or product category (Yellow pages). You can also discover information about web services hosted by a company by examining the technical entities of a UDDI registry (Green pages). In other words, UDDI is an electronic directory that allows organizations to advertise their business and web services and to locate other organizations and web services.

Not only does a UDDI registry provide information about web services and their hosts, a UDDI repository is itself a web service. You can search, access, add, update, and delete information in a UDDI registry using a set of standard SOAP messages. All UDDI registry products must support the standard UDDI data structures and SOAP messages, which means you can access any UDDI-compliant registry using the same standard set of SOAP messages.

Although organizations can set up private UDDI registries, there is a free UDDI registry anyone can use, called the UBR (Universal Business Registry). This registry is accessed at one of four sites hosted by Microsoft, IBM, SAP, and NTT. If you publish information about your company in any one of these sites, the data will be replicated to the each of the other four. You can find out more about the UBR and the sites that host it at http://www.uddi.org.