Research Project: JurWordNet, law semantic lexicon
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There is a two-way relation between semantic lexicon and ontology. A lexicon structured with semantic hierarchies can serve as a basis for a well-build ontology, and ontology is needed, as in our case, to give foundations to lexicon classifications. On the other hand, the distinction between lexicon and ontology is being debated, and it is traceable to the question of the possible language-independent ontology. Some consider WordNet lexicons as ontology, as the net concept are meaning categories, classified on the basis of points of view (perceptions of reality), explicated in language by glosses. As ontology depends on the lexicon or on the language, such comparison implies that each language is able to lexicalize the perception of reality. This concept is hard to accept, especially when one considers that the very top level of taxonomy, and thus the most abstract categories of concepts (entity, mass, matter, shape…) are the hardest to describe in linguistic terms. Often, language applies ontological distinctions within grammar categories, so usually nouns indicate subjects or events, whereas verbs refer to actions, processes, and states, but language behavior is not always consistent with the ontological criterion, and there are no full correspondences among language systems.

In technical dominions, as in the legal one, the correspondence between language objects and ontological entities is unquestionably tighter, as technical terms are accurately described in dictionaries, handbooks, and systematic processing, to build a parallel vocabulary lexicalizing ontological intuitions. Lexicons such as JurWordNet may be considered as light ontology, linguistic extensions of the description of a way of perceiving reality:

It is possible that a lexicon with a semantic hierarchy might serve as the basis for a useful ontology, and an ontology may serve as a grounding for a lexicon. This may be so in technical domains, in which vocabulary and ontology are more closely tied than in more general domains. Hirst 2003, p.14).

Building ontology from lexicon may be a semi-automatic process, drawing from dictionary definitions, syntactical structures, and language strings, from which ontological relations (of subsumption or meronimy) may be obtained. One can scarcely state, though, that these structures are more of an ontological than linguistic nature. In JurWordNet we have favored partially-automatic methods to structure lexicon, and manual connections between lexicon and the classes of Core Legal Ontology, giving some criteria to:

• state what pertains to core ontology, and what to lexicon. The entities of core ontology derive from the suitably integrated top levels of lexical trees. They correspond more or less to the entities that legal authorities, but mostly the legal theory, analyze, define, and systematize: (law, capacity, subject, nullity, crime, contract, representative, malice/fraud, etc.). The ‘object’ itself may be a language concept, for instance, Right, and an entity of ontology. In the first case, it lexicalizes the ontological entity, and, as hypernym, it concentrates classes of concepts and syntagms; in the second case, it interconnects with other entities populating the juridical domain. For instance, it subsumes claim, and contrasts with Duty.

• differentiate the characteristics of lexical relations (synsets) from ontological ones: the semantic relations of lexicon have no inheritability, as they are valid horizontal relations among synsets, while ontological relations express properties and features needed to formally define the class, and are thus inherited and specialized by subclasses. For instance, if there is a dependence relation of mental descriptions on the individual (physical perdurant) as in possession of cognitive capacities, all the subclasses of mental object (will, malice, etc.) inherit the same properties, and others more specific, needed to distinguish them from the general complex. Generally, the glosses used in synsets give a basis to define ontological properties. The ontologically-valid disjunctive relation among classes may not be so on a lexical level: entities pertaining to the same classification are generally disjointed in an ontology, whereas on a language level, syntagms with the same hypernym may overlap: tenancy contract and sale contract are disjointed subclasses of contract, whereas conditional contract is not disjointed from any of the previous ones. The primitive relation between entities of ontology are borrowed from foundational ontology (dependency, participation, constitution…), and supplemented by mediated (composed) relations peculiar to legal dominion. For instance, norm relations of obligation, prohibition, legitimation, etc.

• core ontology does not interrupt the continuum of taxonomic trees toward the top, but in the passage from synsets to ontological classes, relations are suitably replaces. For instance, hypernimy is transformed into an ISA relation (subClassOf) or into an instanceOf one; meronimy into a constitution relation, and the requisites often found within formularized legal definitions, into dependency relations.