Importing WSDL Elements
The import element allows WSDL elements that were separated into independent documents to be imported, as needed, to create a complete document. Different namespaces are used to qualify names in the three elements.
WSDL elements can be imported
As mentioned previously, types, abstract operations, and bindings can be developed independently and combined later to create the complete WSDL file used to describe a particular Web service instance. Thus WSDL allows different data types to be combined with different operations and different bindings. Namespaces are defined for each element, and the tricky part is to ensure that the namespaces don't overlap.
Usefulness of Multiple Transports
Multiple ports means multiple transports for the same service. This flexibility can be handy for the Internet, where some end points might understand MIME but not SOAP, and for an intranet, where some end points will not understand any of the Web protocols or even any standard protocol.
Part of the power of Web services for use inside the enterprise derives from the ability of the services to map easily to multiple protocols and transports through the separation of the binding extensions from the abstract information about a service. WSDL layering clearly separates the abstract definition of a service from its physical, or network, realization and allows for extensions to be defined for any network protocol capable of carrying XML data, or in other words, just about anything. The advantage for a business is that existing transports can be used; Web services do not assume or require that a specific software component has to be installed on each end point.
Multiple schemas may be associated with a particular namespace, and it is up to a processor of XML to determine which one to use in a particular processing context. The WSDL specification provides the processing context via the <import> mechanism, which is based on the XML schema's grammar for the similar concept.