UNIVERSIDAD POLITÉCNICA DE MADRID FACULTAD DE INFORMÁTICA PhD Thesis A DECLARATIVE APPROACH TO ONTOLOGY TRANSLATION WITH KNOWLEDGE PRESERVATION Author: Óscar Corcho Advisor: Asunción Gómez-Pérez April 2004 To myfamily andfriends Acknowledgeiiieiits I would like to thank Asunción Gómez-Pérez for her help and guidance during all these years. Since 1996, when we started working together, we have enjoyed with deep discussions and long struggles about many aspects of the Ontological Engineering field. Besides, Asun has been always able to find a time slot in her extremely busy schedule to help me to structure the thesis contents, to read the early drafts of this document, and to propose many interesting improvements to it so as to make the ideas expressed here easier to understand. I am also in debt with current and oíd members of the Ontological Engineering Group at UPM, with whom I have had many interesting discussions during my and their work and have shared many good moments. Among all of them, I would like to give special thanks to Mariano Femández-López, who made so many helpfiíl comments to improve this thesis, and who gave me important clues about knowledge representation ontologies and about different options for representing translators declaratively; to Rafael González-Cabero, who was in charge of implementing the RDF(S), DAML+OIL and OWL import services for the WebODE workbench and helped me to evalúate the ontology translation method proposed in this thesis; to Ángel López-Cima, who has been patient enough to cope with my frequent programming errors in all the WebODE ontology translation systems developed; and to David Manzano, who made his large mathematical background available to me whenever I needed it. I am particularly indebted to Rosario Plaza Arteche for her valuable help in checking and reviewing the grammar and spelling of the manuscript and improving its clarity and style. Last but not least, I must thank my friends and family for believing in me, and understanding and helping me in my academic career. And among them, I want to thank Katy, for her love and support in everything I do, and for not complaining so much about my constant work during the last period of my thesis work. 111 Abstract In Computer Science, an ontology is defined as a formal explicit specification of a shared conceptualisation. An ontology can be modelled in varied ontology tools, and implemented in varied ontology languages. Different ontology tools and languages are based on different knowledge representation formalisms and provide different ontology components to model ontologies. The ontology translation problem (aka ontology interoperability problem) appears when we decide to reuse an ontology (or part of an ontology) with a tool or language that is different from those ones in which the ontology is available. If we forcé each ontology-based system developer, individually, to commit to the task of translating and incorporating to their systems the ontologies that they need, they will require a lot of effort and time to achieve their objective. This thesis presents two contributions to the current state of the art on ontology translation among languages and/or tools: It proposes a new model for building and maintaining ontology translation systems, characterised by two main features. First, it identifies four layers where ontology translation decisions can be taken: lexical, syntax, semantic, and semiotic. This layered architecture is based on existing work in formal languages and the theory of signs. Second, it proposes to represent ontology translation decisions declaratively. It characterises existing ontology translation approaches from the perspectives of semantic and pragmatic preservation, that is, consequence and intended meaning preservation respectively. It also describes the lifecycle of ontologies in cyclic ontology translation processes, which are defined as successive translations where the initial source and final target formats coincide. Resumen Desde la perspectiva de la informática, una ontologia se define como una especificación formal y explícita de una conceptualización compartida. Las ontologías se pueden modelar con distintos tipos de herramientas e implementar con distintos tipos de lenguajes de ontologías. Estas herramientas y lenguajes pueden estar basados en diferentes formalismos de representación de conocimientos y proporcionar distintos componentes para modelar ontologías. El problema de la traducción o de interoperabilidad de ontologías aparece cuando se decide reutilizar una ontologia (o parte de ella) con una herramienta o lenguaje distinto de aquéllos en los que la ontologia está disponible. Si se fiíerza a cada desarrollador de sistemas basados en ontologías, de manera individual, a realizar la tarea de traducir e incorporar las ontologías que necesitan en sus sistemas, éstos necesitarán gran esfuerzo y tiempo para alcanzar sus objetivos. Esta tesis presenta las siguientes dos contribuciones al estado del arte actual en traducción de ontologías entre lenguajes y/o herramientas: Se propone un nuevo modelo para la construcción y mantenimiento de sistemas de traducción de ontologías. Este modelo se caracteriza, en primer lugar, por ser multicapa: se identifican cuatro capas donde se pueden tomar decisiones de traducción: léxica, sintáctica, semántica y semiótica; esta arquitectura multicapa está basada en el trabajo existente sobre lenguajes formales y la teoría de signos. Asimismo, el modelo propone representar las decisiones de traducción de manera declarativa. Se caracterizan los enfoques de traducción de ontologías existentes desde las perspectivas de la preservación de la semántica y de la pragmática en la traducción. También se describe el ciclo de vida de las ontologías en procesos cíclicos de traducción, que se definen como una secuencia de traducciones sucesivas donde el formato inicial y el final coinciden. vn Tatole ofCoratents Acknowledgements iii Abstract v Resumen vii Table of Contents ix List of Figures xv ListofTables xix Chapter 1 Iníroduction and Overview i Chapter 2 State ofthe Art on Ontological Engineering 7 2.1 What is an ontology? 7 2.2 Which are the main components of an ontology? 11 2.2.1 Modelling heavyweight ontologies using frames and first order logic 11 2.2.2 Modelling heavjrweight ontologies using description logic 12 2.2.3 Modelling lightweight ontologies using software engineering and datábase modelling techniques 14 2.3 Ontology languages 15 2.3.1 Ontology language evolution 15 2.3.2 KR language comparison frameworks 19 2.3.2.1 Formal approaches for KR language comparison 19 2.3.2.2 Semi-formal and informal approaches for KR language comparison 21 2.3.3 Comparison of ontology languages 23 IX 2.4 Ontology tools 26 2.4.1 Ontology development tool evolution 27 2.4.2 Comparison of ontology tools 30 2.5 The ontology translation problem 33 2.5.1 Characterisation of ontology translation problems 33 2.5.2 Translation approaches and architectures 35 2.5.3 Technology for building ontology translation systems 37 2.6 Conclusions 37 Chapter 3 Work Objectives. 39 3.1 Goals and open research problems 39 3.2 Contributions to the state of the art 40 3.3 Work assumptions, hypothesls, and restrictions 42 Chapter 4 A Layered Declarative Ontology Translation Model 47 4.1 Introduction 47 4.2 Ontology translation layers 48 4.2.1 Lexical layer 48 4.2.2 Syntactic layer 51 4.2.3 Semantic layer 53 4.2.3.1 Semantic transformations from combinations of frames and first order logic to description logic 55 4.2.3.2 Semantic transformations from description logic to combinations of frames and first order logic 57 4.2.4 Pragmatic layer 58 4.2.4.1 Pragmatic transformations from combinations of frames and first order logic to description logic 60 4.2.4.2 Pragmatic transformations from description logic to combinations of frames and first order logic 61 4.2.5 Relationships among ontology translation layers 62 4.3 Declarative speciflcation of translation decisions 64 4.3.1 Declarative speciflcation of transformations at the lexical layer 65 4.3.2 Declarative speciflcation of transformations at the syntactic layer 70 4.3.3 Declarative speciflcation of transformations at the semantic and pragmatic layers ... 78 XI 4.4 Method for building an ontology translation system 87 4.4.1 Activity 1. Feasibility study 89 4.4.1.1 Task 1.1. Identify ontology translation system scope 90 4.4.1.2 Task 1.2. Analysis of current ontology translation systems 93 4.4.1.3 Task 1.3. Ontology translation system requirement definition 95 4.4.1.4 Task 1.4. Feasibility decision-making and recommendation 96 4.4.2 Activity 2. Analysis of source and target formats 99 4.4.2.1 Task 2.1. Describe source and target formats 102 4.4.2.2 Task 2.2. Determine expressiveness of source and target formats 104 4.4.2.3 Task 2.3. Compare knowledge models of source and target formats 105 4.4.2.4 Task 2.4. Describe and compare additional features of source and target formats 107 4.4.2.5 Task 2.5. Determine the scope of translation decisions 108 4.4.2.6 Task 2.6. Speciíy test plan 110 4.4.3 Activity 3. Design ofthe translation system 111 4.4.3.1 Task 3.1. Find andreuse similar translation systems 114 4.4.3.2 Task 3.2. Propose transformations at the pragmatic level 115 4.4.3.3 Task 3.3. Propose transformations atthe semantic level 118 4.4.3.4 Task 3.4. Propose transformations atthe syntax level 119 4.4.3.5 Task 3.5. Propose transformations at the lexical level 121 4.4.3.6 Task 3.6. Propose additional transformations 122 4.4.4 Activity 4. Implementation ofthe translation system 123 4.4.4.1 Task 4.1. Find translation fimctions to be reused 127 4.4.4.2 Task 4.2.