A query system (1600) is formed by a wizard (1605) operating to form a data server (1610) arranged to serve data from a data source (1615) to a client application (1630), each of the wizard, the client application, the data server and the data source being linked by a communications network (1650). The data source has native data types and data arranged in a data structure. The wizard operates to firstly identify the data source over the network. The wizard further provides an application program for traversing and examining at least one of the data structure and data of the identified data source. The application program is operable to generate a representative schema (1614) comprising mapping data for converting the native data types to predetermined data types of a common data model. The wizard further operates to create a server application (1612) adapted to use the representative schema to convert the data from the native data types to the predetermined data types and to serve the data to the client application according to the common data model over the network. The representative schema and the server application thereby form the data server generated by the wizard. Once formed, the data server may receive and respond to queries from the client application, which may have no knowledge of the native data types, but which are directed to the data source.