Today's trend is to integrate existing systems in a standard way to make disparate implementations interoperate. Web Services and XML came along with the ability to provide a standard communication interface between these systems, as well as the standard description language - WSDL - the Web Services Description Language that lets those systems define the structure of the services they're providing. Web Services are built using three classic components:
SOAP - Simple Object Access Protocol - the XML-based communication protocol for sending data using Web Services. WSDL - Web Services Description Language - the XML-based language that describes the Web Service that's provided by a particular system and how to access it. UDDI - Universal Description Discovery Integration - a directory that helps to identify dynamically where particular Web Services are and how to find them, as well as a means of publishing services for those who want to provide them.
