Abstract: An application programmer's interface provides a facility for accessing metadata describing the content or attributes of information material. The application programmer's interface comprises a signalling protocol processor operable to receive a metadata string which includes a resource identifier providing an address of a metadata resource, and a file transfer processor operable to provide access to the metadata resource in accordance with a request from the application program. The signalling protocol processor provides an efficient facility for communicating the metadata string. The metadata string may be in the form of a mark-up language such as XML. The metadata resource may be for example a proxy version of the information material, such as a video proxy if the information material is video. Accordingly, the file transfer processor is arranged to provide efficient access to the video proxy using the address provided with metadata string.