Web Services

A Web Service is a Software component stored in one machine that can be accessed by another application in another machine over a network.

Methods in Web Service are invoked through a Remote Procedure Call(RPC).

SOAP (Simple Object Access Protocol) is a platform independant protocol that uses XML to make Remote Procedure Calls.

When a program invokes a Web Method , the request and all relevant info is packaged in a SOAP message and sent to the server where Web Service resides.
A Web Service receives SOAP message, parses its contents to determine the method program wishes to execute and method parameters.
After a web service parses a SOAP message a proper method is called and response is sent back to the client in another SOAP message.

Client and a Web Service communicate using messages, specifically SOAP messages by default. Client sends a SOAP request to a Web Service, and a Web Service method typically returns a SOAP response. Web Services define the type of messages they accept using operations, defined by Web Services Description Language (WSDL). The data that is eventually communicatedover the network must be serialized into XML.

A Web Method tells the .NET that perticular public method should be exposed as a Web-Callable method.

WSDL is written in XML. It is an XML document. It si used to describe Web Services. Used to locate Web Services.

Four major parts of WSDL document
a. WSDL Ports - describes operations that can be performed, messages that are involved.
b WSDL Messages - Defines the data elements of an operation.
c. WSDL Types - Defines the datatype that are used by the Web Service.
d. WSDl Bindings - Defines message format and protocol details for each port.