23.2. UDDI Now we know how to check the temperature or order a pizza. But from whom? What if you wanted to find a weather information service or pizzeria? You might know in the abstract what sort of service (bindings, operations, etc.) you want, but you wouldn't necessarily know how to find all of the relevant service providers. 23.2.1 Finding a service provider Universal Description, Discovery, and Integration (UDDI) is a set of OASIS specifications for the Web services world's equivalent of phone books. When you want to find a service in your town, you pick up the Universal yellow pages business Description listings and scan through them to Discover one that meets your requirements. Then you might Integrate the listing with your wallet by using the "scissors" protocol! UDDI is based on SOAP and WSDL. Service providers use it to let Web services consumers know that their services exist, just as yellow pages help off-line consumers to know that businesses exist. UDDI is different from existing business directories because of its integration with Web services. For instance, a UDDI business registry is actually a Web service itself, so programmers can contact it and ask it questions through SOAP. UDDI and SOAP are also integrated in a more important way. The UDDI registry can report which Web services are available from a particular business. In theory a computer could connect to a UDDI registry, use SOAP to search it for a Web service implementing a "real-time currency conversion" operation, connect to that service and do the conversion without human intervention. The information available through UDDI is typically described as falling into one of three categories, based on the telephone book metaphor: white pages These describe an organization's name, address and contact information. yellow pages Yellow pages categorize businesses by industrial category and geographical location. green pages The so-called green pages are technical descriptions of how to interact with each organization's services. 23.2.2 UDDI data structures A UDDI registry is a database of business entities, business services, binding templates and tModels. These are known as the UDDI data structures. 23.2.2.1 Business entities Business entities are records of corporations or departments. They contain names, contacts, descriptions and other identifying information. A business entity is uniquely identified by a businessKey, which is a long random-looking string of numbers and letters known as a Universally Unique ID (UUID). 23.2.2.2 Business services Business services are records of the services provided by a business entity. These can be true Web services. However, they can just as easily be traditional offline services, such as phone lines, or non-automated services, such as email. Each service has a UUID called a serviceKey. It also has other identifying information, such as a name and a description. Most importantly, each service refers to one or more bindingTemplates. 23.2.2.3 Binding templates Binding templates specify how to contact the company and consume the service. The most important subelement of the binding template is the access point, which tells how to communicate with the service. Valid types of access point are: -
mailto for email, -
http for Web browsers or SOAP, -
https for secure HTTP, -
ftp for File Transfer Protocol, -
fax for fax machine, and -
phone for telephone. 23.2.2.4 tModels tModels[2] are typically used as assertions that a service meets a certain specification. As UDDI is designed to be extremely general, the structure of tModels will vary widely. [2] The word tModel does not really stand for anything. tModels can be used to refer to almost any kind of service description. The description can be as technically precise as a WSDL definition or as informal as a prose document. For Web services, of course, the formal tModels are the useful ones. Other businesses, however, simply cannot be described in that way. What is the input and the output of a dentist? Is biting his finger a fault? 23.2.3 Will it work? The original emphasis in UDDI was on a single public registry for service discovery, now dubbed a Universal Business Registry (UBR).[3] [3] A UBR actually exists; it is operated jointly by IBM, Microsoft, NTT Com, and SAP. The Fourth Edition of The XML Handbook cautioned: Some wonder whether there is even a good reason to think that service discovery will be any different in the Web services world. Perhaps businesses will continue to find one another through advertisements in magazines, introductions through social networks, and other traditional means. Business does require a certain level of trust after all! The UDDI developers appear to have wondered the same thing. UDDI 3.0 recognizes that most of today's Web services are intended for use either internally or among existing trusted trading partners. Accordingly, it provides for multiple registries – private and shared, as well as public – and for their technical interoperability. | 
