Requests for retrieval of data items from another data processing apparatus include embedded objects having executable class functions for performing operations at the target data processing apparatus. This has the advantages of the request implicitly sending data as well as requesting data and allows the request to perform a test on data within an object (such as a comparison with parameters of the request to determine whether the request may be satisfied). Objects within the request may be embedded within each other with different encryption and compression applied to the different objects. As well as achieving communication efficiencies, the ability to selectively encrypt components of a request may be used to provide greater security. For example, a store may be able to interpret the request, while credit details may be separately encrypted such that only a bank may decrypt that subcomponent of the request.