The HPARSE program generates word level lattice files (for use with e.g. HVITE) from a text file syntax description containing a set of rewrite rules based on extended Backus-Naur Form (EBNF). The EBNF rules are used to generate an internal representation of the corresponding finite-state network where HPARSE network nodes represent the words in the network, and are connected via sets of links. This HPARSE network is then converted to HTK V2 word level lattice. The program provides one convenient way of defining such word level lattices.
HPARSE also provides a compatibility mode for use with HPARSE syntax descriptions used in HTK V1.5 where the same format was used to define both the word level syntax and the dictionary. In compatibility mode HPARSE will output the word level portion of such a syntax as an HTK V2 lattice file (via HNET) and the pronuciation information as an HTK V2 dictionary file (via HDICT).
The lattice produced by HPARSE will often contain a number of !NULL nodes in order to reduce the number of arcs in the lattice. The use of such !NULL nodes can both reduce size and increase efficiency when used by recognition programs such as HVITE.