A digital repository 20 includes data items. A user can add additional functionality or program routines to data item by including as a data item a data processing identifier pointing to at least one data processing routine. Such routines are accessed by a client 22 by sending from a client to the digital repository 20 a request to access a data item, wherein the repository provides an interface description document 32 from the digital repository 20 to the client 22 as the response to the request. The client 22 can then transmit a data processing request from the client to a service 26 identified by the data processing identifier of the interface description document 32, the data processing request including the identifier from the interface description document.