Jørgen Fischer Nilsson

Content-based text querying with ontological descriptors

This paper describes a method and a system for content-based querying of texts based on the availability of an ontology for the concepts in the text domain. A key principle in the system is the extraction of conceptual content of noun phrases into descriptors forming an integral part of the ontology.The retrieval of text passages rests on matching descriptors from the text against descriptors from the noun phrases in the query. The match does not need to be exact but is mediated by the ontology invoking in particular taxonomic reasoning with sub- and super-concepts. The paper also reports on a prototype implementation of the system.

Synthesis of Programs in Computational Logic

Since the early days of programming and automated reasoning, researchers have developed methods for systematically constructing programs from their specifications. Especially the last decade has seen a flurry of activities including the advent of specialized conferences, such as LOPSTR, covering the synthesis of programs in computational logic. In this paper we analyze and compare three state-of-the-art methods for synthesizing recursive programs in computational logic. The three approaches are constructive/deductive synthesis, schema-guided synthesis, and inductive synthesis. Our comparison is carried out in a systematic way where, for each approach, we describe the key ideas and synthesize a common running example. In doing so, we explore the synergies between the approaches, which we believe are necessary in order to achieve progress over the next decade in this field.

Ontology-Based Querying

In this paper we introduce an approach to exploit knowledge represented in an ontology in answers to queries to an information base. We assume that the ontology is embedded in a knowledge base covering the domain of the information base. The ontology is first of all to influence ranking of objects in answers to queries as measured by similarity to the query. We consider a generative framework where an ontology in combination with a concept language defines a set of well-formed concepts. Wellformed concepts is assumed to be the basis for an indexing of the information base in the sense that these concepts appear as descriptors attached to objects in the base. Concepts are thus applied to obtain a means for descriptions that generalizes simple word-based information base indexing. In effect query evaluation is generalized to be a matter of comparison at the level of concepts rather than words.

Ontological Extraction of Content for Text Querying

This paper describes a method and a system ONTOQUERY for content-based querying of texts based on the availability of an ontology for the concepts in the text domain. A key principle in the system is the extraction of conceptual content of noun phrases into descriptors forming an integral part of the ontology.The retrieval of text passages rests on matching descriptors from the text against descriptors from the noun phrases in the query. The match need not be exact but is mediated by the ontology, invoking in particular taxonomic reasoning with sub- and super concepts. The paper also reports on a prototype implementation of the system.

Grammatical specification of domain ontologies

This paper presents a formalism supporting the analysis and specification of domain ontologies. The method is founded theoretically on conventional context-free grammars. The use of production rules admits recursive formation of compound categories from given categories subjected to combinability constraints.The proposed domain specification methodology is applied to ontology-guided content-based information retrieval in text databases. It is advanced also as a general purpose methodology for ontological engineering.

Towards a logic programming methodology based on higher-order predicates

This paper outlines a logic programming methodology which applies standardized logic program recursion forms afforded by a system of general purpose recursion schemes. The recursion schemes are conceived of as quasi higher-order predicates which accept predicate arguments, thereby representing parameterized program modules. This use of higher-order predicates is analogous to higher-order functionals in functional programming. However, these quasi higher-order predicates are handled by a metalogic programming technique within ordinary logic programming.Some of the proposed recursion operators are actualizations of mathematical induction principles (e.g. structural induction as generalization of primitive recursion). Others are heuristic schemes for commonly occurring recursive program forms. The intention is to handle all recursions in logic programs through the given repertoire of higher-order predicates.We carry out a pragmatic feasibility study of the proposed recursion operators with respect to the corpus of common textbook logic programs.This pragmatic investigation is accompanied with an analysis of the theoretical expressivity. The main theoretical results concerning computability are(1)Primitive recursive functions can be re-expressed in logic programming by predicates defined solely by non-recursive clauses augmented with afold recursion predicate akin to the fold operators in functional programming.(2)General recursive functions can be re-expressed likewise sincefold allows re-expression of alinrec recursion predicate facilitating linear, unbounded recursion.

Ontology-Based Semantics for Prepositions

This paper addresses the elaboration of a relation-logical compositional semantics for the meaning content of nominals using formal ontologies as semantic domains. Prepositions are conceived as denoting binary semantic role relations between concepts in the ontology. The ontology comes with ontological affinities specifying the admissible ontological combinations. The key idea is to establish a many-many relation between lexical items and nodes in an ontology. This mapping is then systematically extended to phrases, appealing to a relational compositionality principle. The paper focuses on the semantics of prepositions and prepositional phrases, examining in particular disambiguation of nominal phrases containing multiple embedded prepositional phrases, utilizing the ontological affinities. Danish, which offers a rich system of prepositions, is used in the example material.

Inductive Synthesis of Logic Programs by Composition of Combinatory Program Schemes

Based on a variable-free combinatory form of definite clause logic programs we outline a methodology and supporting program environment CombInduce for inducing well-moded logic programs from examples. The combinators comprise fold combinators for recursion on lists. The combinator form is distinguished by enabling piecewise composition of semantically meaningful program elements according to the compositional semantics principle. The principle of combining programs from combinators admits induction of programs without appealing to most-specific-generalization and predicate invention in contrast to prevailing ILP approaches. Moreover, the combinator form avoids confusing object and metavariables in the applied metalogic program environment. In addition useful algebraic rewriting rules can be formulated conveniently with the combinators.

ONTOGRABBING: Extracting Information from Texts Using Generative Ontologies

We describe principles for extracting information from texts using a so-called generative ontology in combination with syntactic analysis. Generative ontologies are introduced as semantic domains for natural language phrases. Generative ontologies extend ordinary finite ontologies with rules for producing recursively shaped terms representing the ontological content (ontological semantics) of NL noun phrases and other phrases. We focus here on achieving a robust, often only partial, ontology-driven parsing of and ascription of semantics to a sentence in the text corpus. The aim of the ontological analysis is primarily to identify paraphrases, thereby achieving a search functionality beyond mere keyword search with synsets. We further envisage use of the generative ontology as a phrase-based rather than word-based browser into text corpora.

Conceptual Pathway Querying of Natural Logic Knowledge Bases from Text Bases

We describe a framework affording computation of conceptual pathways between a pair of terms presented as a query to a text database. In this framework, information is extracted from text sentences and becomes represented in natural logic, which is a form of logic coming much closer to natural language than predicate logic. Natural logic accommodates a variety of scientific parlance, ontologies and domain models. It also supports a semantic net or graph view of the knowledge base. This admits computation of relationships between concepts simultaneously through pathfinding in the knowledge base graph and deductive inference with the stored assertions. We envisage use of the developed pathway functionality, e.g., within bio-, pharma-, and medical sciences for calculating bio-pathways and causal chains.