Section 20.1: 4GL Web Tools Up Chapter 20: Web Services Section 20.3: gSOAP 

20.2 WSDL and SOAP

WSDL is the WWW proposed standard Web Service Description Language - an XML format for defining endpoints, services, and data structures for transmission over the world wide web. A WSDL file is the core file for a web service program.
SOAP (originally Simple Object Access Protocol) is a WWW standard for delivery of web services. These 2 standards work together.
 Section 20.1: 4GL Web Tools Up Chapter 20: Web Services Section 20.3: gSOAP