WSDL
The Web Service Definition Language (WSDL) is an XML extension. It is used to describe the client/server interface that should between web service clients and servers. WSDL is capable of describing:
1.All publicly available methods provided by the service.
2.Data types used in method calls and responses.
3.Information about how to use the underlying transport mechanism (HTTP, FTP etc).
4.The address of the server.
The WSDL file describing a service is stored on a server, perhaps on the registry or the application server. It will be read by the client using a simple HTTP GET exchange.
SAML
Some web service application will be made available to a closed set of users, those who have paid for the service, those who work for particular organisations or those who are known to provide reliable information. The web service standards include the Security Assertion Markup Language (SAML). SAML is a SOAP extension used to provide security functions to web services.
The core idea of SAML is the assertion, a fact about something. For example, there may be an assertion that a particular user has been authenticated. A client uses SAML to request an authentication assertion from a security service. The assertion is then used in subsequent requests to other services.
Client/Server Protocols
The interface provided by the server and used by the client is devised by the designers of the service and described in the WSDL file. The client invokes methods on the server, providing any necessary parameters. The server returns objects in the reply. The protocol is based on SOAP.