Most of the web applicatoins components are currently being developed with web service. It's important to understand the what is web service and how it works?
Web services are application components. They are designed to communicate with open protocols (ie.; XML, SOAP etc). Web services can be implemented on any platform and on any language i.e.; a web service which has originally been developed in Java can be accessed through .NET application.
Web service platform works with 3 different elements SOAP, UDDI, WSDL.
SOAP: SOAP stands for Simple Object Access Protocol. It is a communication protocol and it is a W3C standard. SOAP is designed to communicate through internet. SOAP communicates by sending XML messages. It is simple and extensible. SOAP is platform and language independent protocol.
WSDL: WSDL stands for Web Service Description Language. WSDL is used to locate and describe web services. WSDL is written in XML. This is the key element to develop Web service.
UDDI: UDDI stands for Universal Description, Discovery and Integration. It is a directory of web service interface described by WSDL.