FROM WITTGENSTEIN TO ONTOLOGY ENGINEERING A research framework for ontology-driven AI A framework for future research into Ontology-driven AI, based on analytical language philosophy and cognitive semantics Erik David Johnson www.erk.dk Abstract This thesis establishes how the field of natural language processing (NLP), which is related to artificial intelligence and linguistics, concerned with human-computer interaction, seems to have stagnated, in its strong preference towards statistical methods based on the lower levels of language analysis. As a possible solution, it proposes an alternative approach, which instead has the highest level of language analysis – world knowledge – as its outset. A strategy towards endowing NLP systems with world knowledge through ontology engineering, based on an analysis of the works of language philosopher Ludwig Wittgenstein as related to Lakoff & Johnson’s cognitive semantic theory on the metaphorical systematicity of language, is suggested and tested in a proof-of-concept. The result is a theoretical framework for further research into the development of a top-level ontology for use in high-level NLP systems, based on the cognitive semantic and language philosophical premise established in this thesis, which also includes suggestions for a computational model in the form of artificial neural networks, contextual segmentation using Lakoff’s theory on Frames and metaphor deconstruction and representation using Fauconnier’s Mental Space and Blending Theory. Table of Contents 1 Introduction ..................................................................................................................................................................... 2 1.1 Problem Statement ................................................................................................................................................... 2 1.2 Methodology............................................................................................................................................................ 2 2 A Short Introduction to Natural Language Processing .................................................................................................... 3 3 Levels of Natural Language Analysis.............................................................................................................................. 5 3.1 Morphological Analysis........................................................................................................................................... 6 3.2 Grammatical and Syntactical Analysis .................................................................................................................... 6 3.3 Semantic Analysis.................................................................................................................................................... 8 3.4 Local Discourse Context and Pragmatic Analysis ................................................................................................... 9 3.5 World Knowledge and The Problem of Natural Language Understanding ........................................................... 10 4 Analytical Language Philosophy and World Knowledge.............................................................................................. 13 5 Tractatus Logico-Philosophicus and NLP ..................................................................................................................... 14 5.1 The Basic Ontology of Tractatus ........................................................................................................................... 14 5.2 Wittgenstein’s Picture Theory of Language........................................................................................................... 15 5.3 The Application of Tractatus in NLP..................................................................................................................... 18 6 Philosophical Investigations and NLP ........................................................................................................................... 19 6.1 A different View of Language and Meaning ......................................................................................................... 20 6.2 Language-games: Meaning as Use......................................................................................................................... 21 6.3 Rule-following, life-form and the Acquisition of Language.................................................................................. 21 6.4 The Application of Philosophical Investigations in NLP....................................................................................... 23 7 Common Life-form as a Basis for Patterns of Meaning in NLP.................................................................................... 24 7.1 Wittgenstein's Shift according to Cognitive Theory .............................................................................................. 24 7.2 Embodied Cognition .............................................................................................................................................. 26 8 The Metaphorical Systematicity of Natural Language .................................................................................................. 28 8.1 Our Conceptual System as Metaphorical in Nature ............................................................................................... 28 8.2 Types of Metaphor................................................................................................................................................. 28 8.3 The Philosophy of Metaphor.................................................................................................................................. 30 9 World Knowledge through Ontology Engineering........................................................................................................ 32 9.1 World Knowledge as Ontology.............................................................................................................................. 32 9.2 An Example of Applied Ontology Engineering: Ankiro........................................................................................ 33 9.3 Achieving Generality: Top-level Ontologies ......................................................................................................... 35 9.4 Domain-specific vs. Top-level Ontologies............................................................................................................. 36 10 Proof-of-Concept for a Computational Model of Metaphor ........................................................................................ 38 10.1 Purpose and Limitations....................................................................................................................................... 38 10.2 Computational Model: Artificial Neural Networks.............................................................................................. 39 10.3 Design and Implementation ................................................................................................................................. 42 10.4 Training Data ....................................................................................................................................................... 45 10.5 Performance and Experiments ............................................................................................................................. 46 10.6 Evaluation and Discussion................................................................................................................................... 48 11 Building upon Metaphor: Multi-level Contextuality ................................................................................................... 52 11.1 The Problem of Natural Language Understanding – Revisited............................................................................ 52 11.2 Natural Language: More than Metaphor.............................................................................................................. 53 11.3 The Contextual Granularity of Wittgenstein’s Language Games ........................................................................ 56 11.4 Contextual Segmentation using Frames............................................................................................................... 57 11.5 Mental Space and Blending Theory..................................................................................................................... 59 12 A New Approach to Ontology Engineering and World Knowledge............................................................................ 62 12.1 Results and Suggested Areas for Further Research.............................................................................................. 62 12.2 Academic Validation and Verification................................................................................................................. 65 13 Conclusion................................................................................................................................................................... 66 References ........................................................................................................................................................................ 69 Appendices ......................................................................................................................................................................