Q 1. What is a Web service?
A.A Web services is a piece of software that you can interact with using an XML message format. This message format is usually SOAP (Simple Object Access Protocol), though alternatives exist (e.g. XML-RPC, REST).
Other than SOAP, there a number of other standards that can be used by your Web services and their clients. The interface provided by a Web service is often defined using another XML format called WSDL. A WSDL description can be shared with a Web service client in many ways, but the recommended way is to use a registry to publish it. UDDI (Universal Discovery Description and Integration) is a specification of a Web service registry that is industry accepted. UDDI registries can be hosted internal to a company or a group of companies and used for looking up Web services, much the same way a LDAP directory is. There is also a global UDDI registry, called a UBR (Universal Business Registry), that is hosted by IBM, Microsoft, SAP and Fujitsu. Interestingly, a UDDI registry is itself a Web service- searching and publishing to the registry can be done using SOAP messages.
Besides WSDL and UDDI, there are a number of other Web service standards and specifications that deal with issues like security, composing Web services, Transactions etc.