The invention provides a time-efficient way of performing a query in a database or information retrieval system comprising operations such as intersection, union, difference and exclusive disjunction on two or more sets of keys stored in a database or information retrieval system. In a novel execution model, all data sources are tries. Two or more input tries are combined in accordance with the respective set operation, to obtain the set of keys associated with the nodes of a respective resulting trie. An intersection operation performed in this way can be used for efficient range queries, in particular when two or more data items are involved in the query. The physical algebra of the implementation of tries based on bitmaps corresponds directly to the logical algebra for the set operations and allows for efficient implementation by means of bitwise Boolean operations.