A parser for parsing documents comprising a Document Order List Creator, a YPath Table Creator, and a ZPath Table Creator. The arrangement of the Document Order List creator being such that it is adapted to produce a Document Order List (DOL) correlating a unique index number with an associated node, and the Document Order List creator being adapted to allocate each node in a document parsed its own unique index number in the DOL. The arrangement of the YPath Table Creator is such that it is adapted to produce a YPath Table having a set of sequences of node names representative of all sequences of node names encountered in traversing from the root node to all possible nodes in the document parsed, and associated with each sequence of node names a corresponding group of index numbers corresponding to the index numbers in the DOL for which the associated sequence of node names is true. The arrangement of the ZPath Table Creator is adapted to create a ZPath Table having a set of sequences of ordinals representative of ordinals of those nodes encounterable in traversing from the root node to all possible nodes in the document, the ordinal of a node being the integer value position of the node amongst those nodes of the same name which share the same parent node, and associated with each set of sequences of ordinals, a corresponding group of index numbers corresponding to the index numbers in the DOL for which the associated sequence of ordinals for nodes is true.