A clustering approach to automatic verb classification incorporating selectional preferences: model, implementation, and user manual

This report presents two variations of an innovative, complex approach to semantic verb classes that relies on selectional preferences as verb properties. The underlying linguistic assumption for this verb class model is that verbs which agree on their selectional preferences belong to a common semantic class. The model is implemented as a soft-clustering approach, in order to capture the polysemy of the verbs. The training procedure uses the Expectation-Maximisation (EM) algorithm (Baum, 1972) to iteratively improve the probabilistic parameters of the model, and applies the Minimum Description Length (MDL) principle (Rissanen, 1978) to induce WordNet-based selectional preferences for arguments within subcategorisation frames. One variation of the MDL principle replicates a standard MDL approach by Li and Abe (1998), the other variation presents an improved pruning strategy that outperforms the standard implementation considerably. Our model is potentially useful for lexical induction (e.g., verb senses, subcategorisation and selectional preferences, collocations, and verb alternations), and for NLP applications in sparse data situations. We demonstrate the usefulness of the model by a standard evaluation (pseudo-word disambiguation), and three applications (selectional preference induction, verb sense disambiguation, and semi-supervised sense labelling)

Die Semantik von projektiven Lokativausdrücken: eine empirische Evaluierung von geometrischen Bedingungen

This thesis presents a method for evaluating semantic theories of projective locative expressions such as "X is above Y" and "X to the right of Y". The method is implemented for semantic theories that represent meaning of projective locative expressions in terms of geometrical constraints in two-dimensional space. A set of semantic theories is defined according to proposals from the literature. These theories predict precise geometrical constraints for projective locative expressions. Furthermore, a formalism is proposed which is used to combine these theories in order to generate new semantic theories that are capable of handling vagueness of projective locative expressions. The empirical basis of the evaluation is a set of expressions that subjects of a "map task" experiment (Anderson et al., 1991) have used to describe spatial relations in two-dimensional space. Each expression refers to a specific map of which two-dimensional geometrical representations are derived. The semantic theories are tested with these data by checking whether the geometrical constraints predicted for an expression are satisfied by the corresponding geometrical representation. The evaluations show good results for most theories which have been proposed in the literature. The results are systematically improved by the corresponding theories that handle vagueness.Diese Arbeit stellt eine Methode zur Evaluierung von Bedeutungstheorien über projektive Lokativausdrücke, wie zum Beispiel "X ist über Y" und "X ist rechts von Y", vor. Diese Methode wird auf Bedeutungstheorien angewendet, die die Bedeutung von projektiven Lokativausdrücken als geometrische Beschränkungen im zwei-dimensionalen Raum darstellen. Eine Menge von Bedeutungstheorien wird entsprechend von Vorschlägen aus der Literatur definiert. Diese Theorien machen präzise Voraussagen darüber, welche geometrischen Beschränkungen mit projektiven Lokativausdrücken einhergehen. Des Weiteren wird ein Formalismus vorgeschlagen, mit dem Paare dieser Theorien zu neuen Theorien kombiniert werden können. In Gegensatz zur ihren Teilen modellieren diese neuen Theorien Vagheit von projektiven Lokativausdrücken. Die empirische Grundlage für die Evaluierung bildet eine Menge von Ausdrücken, die Probanden eines "Maptask"-Experiments (Anderson et al., 1991) benutzt haben, um räumliche Relationen im zwei-dimensionalen Raum zu beschreiben. Jeder Ausdruck bezieht sich auf eine bestimmte Karte, aus welcher zwei-dimensionale geometrische Repräsentationen für die Evaluierung hergeleitet wurden. Die Bedeutungstheorien werden mit diesen Daten getestet, indem überprüft wird, ob die geometrischen Bedingungen, die sie für einen Ausdruck bestimmt, von der entsprechenden geometrischen Repräsentation erfüllt werden. Die Evaluierung zeigt gute Ergebnisse für die meisten in der Literatur vorgeschlagenen Bedeutungstheorien. Die Ergebnisse werden systematisch durch die entsprechenden Theorien, die Vagheit modellieren, verbessert

Semantics of Projective Locative Expressions: An Empirical Evaluation of Geometrical Conditions

This thesis presents a method for evaluating semantic theories of projective locative expressions such as ’X is above Y ’ and ’X is to the right of Y’. The method is implemented for semantic theories that represent meaning of projective locative expressions in terms of geometrical constraints in two-dimensional space. A set of semantic theories is defined according to proposals from the literature. These theories predict precise geometrical constraints for projective locative expressions. Furthermore, a formalism is proposed which is used to combine these theories in order to generate new semantic theories that are capable of handling vagueness of projective locative expressions. The empirical basis of the evaluation is a set of expressions that subjects of a ’map task ’ experiment (Anderson et al., 1991) have used to describe spatial relations in two-dimensional space. Each expression refers to a specific map of which two-dimensional geometrical representations ar