1. A method of interacting with a scema-defined service by a terminal device over a network, the method comprising the steps of: receiving a request network message for establishing communication between the service and the device; sending in response to the request network message a component application program including a plurality of components, a first set of the components having descriptors expressed in a structured definition language and a second set of the components being expressed as a series of instructions, the components being configured for provisioning by a runtime environment of the device to produce an executable version of the component application program configuring the device as a client of the service; wherein execution of the executable version provides for a subsequent exchange of information over the network between the service and the device.