1. A stored data access controller, configured to control access to data items encoding graph data and stored in a data storage apparatus, each data item being composed of data values encoding a labelled link between a subject graph node and an object graph node; the stored data access controller comprising: a query module, configured to receive a query requesting, as a query result, a specified subset of the data items stored in the data storage apparatus, and configured to obtain data items belonging to the specified subset from the data storage apparatus as a preliminary query result; a suppression module, configured to obtain the preliminary query result from the query module, to generate a revised version of the preliminary query result by selectively suppressing information from the preliminary query result, and to output, as the requested query result in response to the received query, the revised version of the preliminary query result; wherein selectively suppressing information comprises, for the or each of one or more graph nodes, suppressing the data value representing the graph node in accordance with access control information attributed to the label of a labelled link between the graph node and another graph node, the graph node being either the subject graph node or the object graph node linked by the labelled link.