Towards Recursive Models -- A Computational Formalism for the Semantics of Temporal Presuppositions and Counterfactuals in Natural Language

The linguistic phenomena of temporal presuppositions and counterfactuals, situated on the boundary line between semantics and pragmatics, are common to many languages, and the computational treatment of such phenomena is difficult because of their nonmonotonic aspect. These phenomena are presented through a corpus of examples; they are studied emphasizing the various types of knowledge underlying them; and the fragment of language that encloses such phenomena is defined in a way not dependent from a specific language. Then, Recursive Models, a formalism for modeling the semantics of utterances containing temporal presuppositions and counterfactuals, are proposed, described from both functional (by formal specifications) and structural points of view, and compared with related work. Finally, the adequacy of Recursive Models is empirically verified: TOBI (Temporal presuppositions and counterfactuals: an Ontological Based Interpreter), a system that interacts with the user in natural language using the recursive models, is illustrated. TOBI is not based on a deductive system, but uses the more primitive and flexible notion of model-based evaluation; its architecture, flow of control and internal data structures are presented

Towards Recursive Models - A Computational Formalism for the Semantics of Temporal Presuppositions and Counterfactuals in Natural Language

syntax In order to analyze the above introduced phenomena, it is sufficient to work on a restricted language fragment, defined in this section. The usual way to formally define a fragment of the language is to provide a grammar. Since the considered phenomena occur in many natural languages (almost every western language has the syntactic constructs necessary for expressing the previous utterances), I prefer here a more abstract description, to some extent independent from the particular language adopted. I shall call such formalism abstract syntax. The first step to define the abstract syntax of the relevant natural language fragment (that will be denoted with L) is to specify a family of syntactic functions, functions that syntactically manipulate sentences of the natural language to obtain other sentences. The definition of the abstract syntax of L is then obtained by means of a set hierarchy: starting from a set of simple sentences, other sets containing complex and compound se..