1. A data processing method comprising: providing a data model having a set of entity types and a set of attributes for each entity type for the set of entity types; providing customizing data for the data model, the customizing data indicating data sources for the attributes and describing data structures being provided by the data sources; querying attribute data for at least a first attribute of the set of attributes of one of the entity types; determining, from the customizing data, if a single data source for the first attribute data of the one of the entity types is available; if such a single data source is not available, determining at least first and second ones of the data sources, which in combination, comprise the first attribute data of the one of the entity types; generating a sub-query for each one of the at least first and second data sources; and combining the results of the sub-queries to provide a query result.