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Section: Software

LEOPAR

Participants : Bruno Guillaume [correspondant] , Guy Perrier, Mathieu Morey, Paul Masson.

Software description

LEOPAR is a parser for natural languages which is based on the formalism of Interaction Grammars  [35] . It uses a parsing principle, called “electrostatic parsing” which consists in neutralizing opposite polarities. A positive polarity corresponds to an available linguistic feature and a negative one to an expected feature.

Parsing a sentence with an Interaction Grammar consists in first selecting a lexical entry for each of its words. A lexical entry is an underspecified syntactic tree, a tree description in other words. Then, all selected tree descriptions are combined by partial superposition guided by the aim of neutralizing polarities: two opposite polarities are neutralized by merging their support nodes. Parsing succeeds if the process ends with a minimal and neutral tree. As IGs are based on polarities and under-specified trees, LEOPAR uses some specific and non-trivial data-structures and algorithms.

The electrostatic principle has been intensively considered in LEOPAR. The theoretical problem of parsing IGs is NP-complete; the nondeterminism usually associated to NP-completeness is present at two levels: when a description for each word is selected from the lexicon, and when a choice of which nodes to merge is made. Polarities have shown their efficiency in pruning the search tree:

Current state of the implementation

LEOPAR is presented and documented at http://leopar.loria.fr ; an online demonstration page can be found at http://leopar.loria.fr/demo .

It is open-source (under the CECILL License http://www.cecill.info ) and it is developed using the InriaGforge platform (http://gforge.inria.fr/projects/semagramme/ )

The main features of current software are:

During 2011, with the help of an engineer, the LEOPAR software was improved in several ways: