Web Service Development Workflow

Contract first is a good way between two systems, each provided by different suppliers (which imply possibly different vendor)

"Contract First Web Services Interoperability between Microsoft .NET and IBM WebSphere"
http://msdn.microsoft.com/vstudio/java/interop/websphereinterop/default.aspx

The workflow is basically: define the data schema being exchanged (basically XSD), write the WSDL, then one side implements the client, one side implements the service. VS.NET user can make use of wsdl.exe to generate both the client proxy and server stub (for eg an internal testing simulator) easily.

Thus, concreting the contract is essential. WSDL basically serves as the contact, like alternative IRS (Interface Requirement Specification).

Some background info on WSDL, a collapsed view of WSDL file defines,

<types> - basically data type definition, but expressed in terms of XSD
<message> - data (expressed in the 'types') being exchanged for each web service method
<portType> - operations (expressed in terms of 'message')
<binding> - when operations is bound to a particular protocol (Soap, HttpGet, HttpPost), expressed in terms of 'portType'
<service> - finally, binding has to be associated on a physical network address

Simple: it is basically some sort of layered definition.

Thus, concreting the contract is essential. WSDL basically serves as the contact, like alternative IRS (Interface Requirement Specification).

Some background info on WSDL, a collapsed view of WSDL file defines,

<types> - basically data type definition, but expressed in terms of XSD
<message> - data (expressed in the 'types') being exchanged for each web service method
<portType> - operations (expressed in terms of 'message')
<binding> - when operations is bound to a particular protocol (Soap, HttpGet, HttpPost), expressed in terms of 'portType'
<service> - finally, binding has to be associated on a physical network address

Simple: it is basically some sort of layered definition.