1. A visualization system for producing a visualization, information relating to a task being performed in the visualization system being displayed in the visualization in response to occurrence of an event in the visualization system, the displayed information having as its source a data item instance in an event instance representing the event and being selected from the data item instance as determined by a task instance representing the task and the visualization system being implemented in a data processing system, wherein the data processing system accesses an ontology contained in a storage device, the data processing system using the ontology to determine relationships between instances of objects having types and the ontology comprising: a set of ontology objects, the set of ontology objects describing the types and relationships therebetween; and an accelerator that accelerates a determination by the data processing system of a set of types that are relevant to a particular type, wherein the instances of objects are the data item instance and the task instance, the particular type is the type of the data item instance, and the set of types includes the type of the task instance and the visualization system applies the type of the task instance and the type of the data item instance to the ontology to determine what information is to be selected from the data item instance.