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Manolis Koubarakis

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12 papers
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12

AAAI Conference 2014 Conference Paper

A Reasoner for the RCC-5 and RCC-8 Calculi Extended with Constants

  • Stella Giannakopoulou
  • Charalampos Nikolaou
  • Manolis Koubarakis

The problem of checking the consistency of spatial calculi that contain both unknown and known entities (constants, i. e. , real geometries) has recently been studied. Until now, all the approaches are theoretical and no implementation has been proposed. In this paper we present the first reasoner that takes as input RCC-5 or RCC-8 networks with variables and constants and decides their consistency. We investigate the performance of the reasoner experimentally using real-world networks and show that we can achieve significantly better times by geometry simplification and parallelization.

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AAAI Conference 2014 Conference Paper

Fast Consistency Checking of Very Large Real-World RCC-8 Constraint Networks Using Graph Partitioning

  • Charalampos Nikolaou
  • Manolis Koubarakis

We present a new reasoner for RCC-8 constraint networks, called gp-rcc8, that is based on the patchwork property of path-consistent tractable RCC-8 networks and graph partitioning. We compare gp-rcc8 with state of the art reasoners that are based on constraint propagation and backtracking search as well as one that is based on graph partitioning and SAT solving. Our evaluation considers very large realworld RCC-8 networks and medium-sized synthetic ones, and shows that gp-rcc8 outperforms the other reasoners for these networks, while it is less efficient for smaller networks.

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TIME Conference 2004 Invited Paper

Word Proximity Constraints: Information Retrieval Meets Temporal Reasoning

  • Manolis Koubarakis

We study the data models WP and AWP that have been widely used for many years in the area of information retrieval. WP and AWP can be used to represent and query textual information under the Boolean model using the concepts of attributes with values of type text, and word proximity constraints. Variations of WP and AWP are in use in most deployed digital libraries using the Boolean model, text extenders for relational database systems (e. g. , Oracle text) and the search engine Altavista. We present the syntax, semantics and model theory of WP and AWP and analyze the complexity of query satisfiability and entailment. Since word proximity constraints are very similar to temporal constraints, the techniques we use in our analysis are similar to the ones developed in previous work on first-order theories of temporal constraints and temporal constraint databases.

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AAAI Conference 1999 Conference Paper

Querying Temporal Constraint Networks in PTIME

  • Manolis Koubarakis
  • University of Athens
  • Spiros Skiadopoulos
  • National Technical University of Athens

Westart with the assumption that temporal knowledgeusually captured by constraint networks can be represented and queried more effectively by using the schemeof indefinite constraint databases proposed by Koubarakis. Althoughquery evaluation in this scheme is in general a hard computational problem, we demonstrate that there are several interesting cases where query evaluation can be done in PTIME. Thesetractability results are original and subsumeprevious results by van Beck, Brusoni, Console andTerenziani.

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