A database controller controls a database for storing graph data encoded as triples, each triple having a subject, a predicate, and an object, and each stored within a data item among a set of data items ordered according to the triple stored within. Each data item is stored on a storage node from among a plurality of storage nodes distributed in a network. The database controller includes a storage request receiver configured to receive a request to store a triple in the database, and a data item generation module configured to generate two or more data items each having a different version of the triple.