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. The address may be a Uniform Resource Identifier address allowing access to the resource from any network linked via the World Wide Web. The application programmer's interface therefore provides a standard interface format for making metadata and metadata resources available to application programs.