Episodic Logic Meets Little Red Riding Hood: A Comprehensive, Natural Representation for Language Un

We describe a comprehensive framework for narrative understanding based on Episodic Logic (EL). This situational logic was developed and implemented as a semantic representation and commonsense knowledge representation that would serve the full range of interpretive and inferential needs of general NLU. The most distinctive feature of EL is its natural language-like expressiveness. It allows for generalized quantifiers, lambda abstraction, sentence and predicate modifiers, sentence and predicate reification, intensional predicates (corresponding to wanting, believing, making, etc.), unreliable generalizations, and perhaps most importantly, explicit situational variables (denoting episodes, events, states of affairs, etc.) linked to arbitrary formulas that describe them. These allow episodes to be explicitly related in terms of part-whole, temporal and causal relations. Episodic logical form is easily computed from surface syntax and lends itself to effective inference. The Centrality of Representation in NLP Language understanding is an organic phenomenon, and the various stages or facets of the language understanding process — parsing, computing a representation, making inferences, etc. — should not be considered in isolation from each other. For instance, both during the computation of utterance meaning and upon its completion, a great deal of “spontaneous,” input-driven inferencing is presumed to occur, working out plausible interpretations and consequences based on the discourse interpreted so far, and on meaning postulates and world knowledge. This includes computing unique referents for referring expressions, predictions, and explanations which ultimately give a causally coherent elaboration of what has been said. Therefore, an essential requirement is that the representation support such inferences and the knowledge behind them. It should do so in a way that is both intuitively transparent and analyzable in terms of a formal notion of interpretation. The formal interpretability of the representation allows us to examine in detail whether it captures meanings as intended, and whether proposed inference rules are semantically justifiable. These considerations point to the centrality of the issue of representation. The ease of mapping from syntax to a semantic representation, “deindexing” (amalgamating the context information into the representation of an utterance so that the resulting representation becomes context-independent), and performing inferences all depend on the representation used. A basic methodological assumption of our work is that these multiple demands on the representation are best met by using a highly expressive logic closely related to NL itself. The possibility of handling tense, causes, facts, modifiers, propositions, beliefs, etc., simply and directly depends on the expressiveness of the representation. To see the importance of this issue, let us consider the following excerpt from the story of Little Red Riding Hood . In our later discussion of test scenarios, the wording is slightly different, as we were rather haphazardly using several children’s books. One source was (Perrault, 1961).