1. Method of synchronizing a data processing device ( 9 - 11 ) with a data processing system ( 1 ) to which the data processing device ( 9 - 11 ) has an intermittent connection, including: determining a first context based on variable data, determining a second context, valid over a longer term than the first context, based on further data, and using both the first and the second context to control a synchronization process during which data is communicated between the data processing device ( 9 - 11 ) and the data processing system ( 1 ), and which results in at least one of them obtaining a target set of data, wherein the target set of data is determined in such a way that its composition is based on both the first and the second context.