Providing a context-based service to a terminal, including: a) receiving a query from a service application, the query indicating that a context server should perform an action when a query condition is fulfilled, the query condition referring to one or more attributes of derived context information indicative of a context of the terminal; b) generating a query evaluation trigger indicating that the query condition should be evaluated; c) identifying raw context information to derive the derived context information; d) generating a calculation trigger indicating that the derived context information should be calculated when the raw context information is updated; e) receiving an update of the raw context information and, according to the calculation trigger, calculating a new value of the derived context information; and f) according to the query evaluation trigger, evaluating the query condition by using the new value and, if the query condition is fulfilled, performing the action.