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Lenhart Schubert

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6 papers
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6

AAAI Conference 2015 Conference Paper

Semantic Representation

  • Lenhart Schubert

In recent years, there has been renewed interest in the NLP community in genuine language understanding and dialogue. Thus the long-standing issue of how the semantic content of language should be represented is reentering the communal discussion. This paper provides a brief “opinionated survey” of broadcoverage semantic representation (SR). It suggests multiple desiderata for such representations, and then outlines more than a dozen approaches to SR–some longstanding, and some more recent, providing quick characterizations, pros, cons, and some comments on implementations.

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AAAI Conference 2006 Conference Paper

Turing’s Dream and the Knowledge Challenge

  • Lenhart Schubert

There is a set of clear-cut challenges, all centering around knowledge, that have received insufficient attention in AI, and whose solution could bring the realization of Turing's dream -- the dream of a machine we can talk with just like a person, and which is therefore (at least) our intellectual equal. These challenges have to do with the representation of linguistically expressible knowledge, the role of knowledge in language understanding, the use of knowledge for several sorts of commonsense reasoning, and knowledge accumulation. Concerning the last topic, I briefly present preliminary results of some of our recent efforts to extract "shallow" general knowledge about the world from large text corpora.

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AIJ Journal 1995 Journal Article

Efficient algorithms for qualitative reasoning about time

  • Alfonso Gerevini
  • Lenhart Schubert

Reasoning about temporal information is an important task in many areas of Artificial Intelligence. In this paper we address the problem of scalability in temporal reasoning by providing a collection of new algorithms for efficiently managing large sets of qualitative temporal relations. We focus on the class of relations forming the Point Algebra (PA-relations) and on a major extension to include binary disjunctions of PA-relations (PA-disjunctions). Such disjunctions add a great deal of expressive power, including the ability to stipulate disjointness of temporal intervals, which is important in planning applications. Our representation of time is based on timegraphs, graphs partitioned into a set of chains on which the search is supported by a metagraph data structure. The approach is an extension of the time representation proposed by Schubert, Taugher and Miller in the context of story comprehension. The algorithms herein enable construction of a timegraph from a given set of PA-relations, querying a timegraph, and efficiently checking the consistency of a timegraph augmented by a set of PA-disjunctions. Experimental results illustrate the efficiency of the proposed approach.

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AIJ Journal 1994 Journal Article

On point-based temporal disjointness

  • Alfonso Gerevini
  • Lenhart Schubert

We address the problems of determining consistency and of finding a solution for sets of three-point relations expressing exclusion of a point from an interval, and for sets of four-point relations expressing interval disjointness. Availability of these relations is an important requirement for dealing with the sorts of temporal constraints encountered in many AI applications such as plan reasoning. We prove that consistency testing is NP-complete and finding a solution is NP-hard.

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