Abstract: A communications system query processing element, for example a home location register for a mobile communications system, includes a plurality of application processors. First data such as permanent data relating to a plurality of mobile subscribers (subscription information etc.) is available at all application processors, whereas second data such as temporary data relating to the plurality of subscription is partitioned between the application processors. Queries are allocated via a transaction bus to an available application processor. If it is not the correct one for the subscriber originating the query, it is redirected via the transaction bus. This arrangement permits a linear growth in terms of database to be achieved with increasing numbers of subscribers by the addition of application processors as necessary and in a manner not involving a processing bottleneck.