1. A computer-implemented query system for carrying out a query process corresponding to a received query element on a database system and/or a search-engine system, the query system comprising: a synchronisation unit, comprising a processor, operable, as a non-text-centric synchronisation process, to convert a non-text-centric data entry of the database system into a corresponding text-centric data entry representative of the non-text-centric data entry, and to enter the text-centric data entry into an index of the search-engine system making the non-text-centric data entry of the database system available to both the search-engine and database systems; a query-dividing unit operable to divide a received query into a plurality of component query elements, the query system being operable to carry out a query process per query element; an analyzing unit operable, for each query element, to analyze the query element for use in carrying out the query process corresponding to that query element; a determining unit operable to determine, for each query element in dependence upon such analysis, whether to carry out the query process on the database system and/or the search-engine system; and an execution unit operable, for each query element, to carry out the query process directly on the database system without using the index of the search-engine system, when it is determined that the query process is to be carried out on the database system, and/or directly on the search-engine system using the index of the search-engine system, when it is determined that the query process is to be carried out on the search-engine system, wherein: the synchronisation unit is operable in said non-text-centric synchronisation process to enter the text-centric data entry into the index of the search-engine system together with correspondence information associating each index entry in the index resulting from that text-centric data entry to its corresponding non-text-centric data entry of the database system, and, when a change is made to information searchable by said query system, to cause the change to be represented in both the database system and the search-engine system; and the determining unit is operable, for each query element, if the analysis indicates that the query element relates to a search expression supported by the database system, to determine that the query process is to be carried out on the database system, and, if the analysis indicates that the query element relates to a search expression not supported by the database system but supported by the search-engine system, to determine that the query process is to be carried out on the search-engine system.