A web service request is received by an intermediary that performs a conversion of the requestor's service interface to the service interface supported by a service provider matching the requested service, then invokes that service. A reverse conversion is performed when passing a reply to the requester. The web serving intermediary maintains a library of each target service in terms of the target service's tModel and on its binding protocol support. The intermediary receives web service requests from requestors including their source tModel and target web service information. The intermediary identifies a mapping aspect to invoke the target web service from the aspect library. The target service tModel is embodied in the mapping aspect which is weaved into the code invoking the target service at runtime. In this way, the interface logic is decided at run time.