1. A data processing apparatus for comparing a first object, associated with said data processing apparatus, with a second object, associated with a remote data processing apparatus, said data processing apparatus comprising: an input device operable to accept a first and a second set of data associated with said first object, said first set of data describing said first object and said second set of data describing a third object; a memory, wherein said memory is adapted to store said first and said second set of data; a receiver, wherein said receiver is adapted to obtain a first subset of a third and a fourth set of data, respectively, from said remote data processing apparatus, said third and said fourth set of data being associated with said second object, said third set of data describing said second object and said fourth set of data describing a fourth object; a transmitter, wherein said transmitter is adapted to send a first subset of said first and said second set of data, respectively, to said remote data processing apparatus; and a processor, wherein said processor is adapted to perform correlation analysis between said first subsets of said first and said fourth set of data, respectively, to obtain a first value of correlation between said first and said second object, and correlation analysis between said first subsets of said second and said third set of data, respectively, to obtain a second value of correlation between said first and said second object.