Title:  Automated Spatial Semantic Analysis Towards Commonsense Reasoning（徐超）、Losing Connection: the Modal Logic of Definable Link Deletion（李大柱）

Speaker: 徐超、李大柱

Time:  29 OCT, 2019, 15:10-18:00

Place:   Classroom 406, Second Teaching Building, PKU

Abstract:

徐超：

       Modeling and analyzing spatial dynamics is key to next-generation commonsense reasoning systems. Automatically extracting spatial information from natural language, i.e., detecting objects of spatial scenes and relations holding between them, could considerably boost such systems. The field of cognitive linguistics has actively provided theories and cognitive models to tackle this challenge. However, existing solutions tend to focus on specific word classes, domains of discourse, or machine learning techniques that do not provide human-understandable explanations for their decisions. In this paper, we propose to unify methods of automated spatial information extraction with cognitive models, bringing together construction theory, cognitive frameworks on spatial language, and image schemas. This unified framework finds practical application in a proposed rule-based and fully explainable approach to automatically detect spatial information in natural language, evaluated on the standard datasets CLEF-2017 with best-performing results.

李大柱：

         In this talk, we start with a two-player game that models communication under adverse circumstances in everyday life and study it from the perspective of a modal logic of graphs, where links can be deleted locally according to definitions available to the adversarial player. We first introduce a new language, semantics, and some typical validities. We then formulate a new type of first-order translation for this modal logic and prove its correctness. Then, a novel notion of bisimulation is proposed which leads to a characterization theorem for the logic as a fragment of first-order logic, and a further investigation is made of its expressive power against hybrid modal languages. Next, we discuss how to axiomatize this logic of link deletion, using dynamic-epistemic logics as a contrast. Finally, we show that our new modal logic lacks both the tree model property and the finite model property, and that its satisfiability problem is undecidable.