A data structure is provided for annotating data files within a database. The annotation data comprises a phoneme and word lattice which allows the quick and efficient searching of data files within the database, in response to a user's input query for desired information. The phoneme and word lattice comprises a plurality of time-ordered nodes, and a plurality of links extending between the nodes. Each link has a phoneme or word associated with it. The nodes are arranged in a sequence of time-ordered blocks such that further data can be conveniently added to the lattice.