View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Glamorgan Dspace Discrete event calculus using Semantic Web technologies WILL MEPHAM A submission presented in partial fulfilment of the requirements of the University of Glamorgan/Prifysgol Morgannwg for the degree of Doctor of Philosophy 2010 Table of Contents ABSTRACT................................................................................................................................................1 GLOSSARY................................................................................................................................................2 CHAPTER 1 OBJECTIVES AND MOTIVATION.................................................................................4 1.1 BACKGROUND TO THE PROJECT...................................................................................................................4 1.2 MOTIVATION...........................................................................................................................................5 1.3 INITIAL GOALS.........................................................................................................................................7 1.3.1 A DEC ontology defined in Semantic Web languages.................................................................7 1.3.2 A software framework that can use the ontology for practical applications..............................8 1.3.3 An accurate implementation of DEC..........................................................................................8 1.3.4 A reusable framework for DEC rule resolution..........................................................................9 1.3.5 An investigation into merging time ontology with DEC ............................................................9 1.4 LONG TERM OBJECTIVES............................................................................................................................9 CHAPTER 2 LITERATURE REVIEW.................................................................................................11 2.1 OVERVIEW............................................................................................................................................11 2.1.1 Scope of this section..................................................................................................................11 2.1.2 Preliminary discussion..............................................................................................................11 2.1.2.1 References to Semantic Web standards.............................................................................................11 2.1.2.2 Logic terms......................................................................................................................................11 2.1.2.3 Rules................................................................................................................................................11 2.2 BACKGROUND TO THE SEMANTIC WEB.....................................................................................................11 2.3 ONTOLOGY AND THE SEMANTIC WEB.......................................................................................................14 2.3.1 Different interpretations of ontology.........................................................................................14 2.3.2 Motivation for ontology engineering........................................................................................15 2.3.3 Semantic web standards............................................................................................................16 2.3.4 Semantic web stack...................................................................................................................18 2.4 RULES AND THE SEMANTIC WEB.............................................................................................................22 2.4.1 The need for rules in Semantic Web applications.....................................................................22 2.4.2 SWRL.........................................................................................................................................22 2.4.3 Decidability and rules...............................................................................................................23 2.5 EVENT CALCULUS IN THE CONTEXT OF TEMPORAL REASONING......................................................................25 2.5.1 Common concerns of temporal logics.......................................................................................25 2.5.1.1 Representation of intervals and timepoints.......................................................................................25 2.5.1.2 Cause and effect for temporal logics................................................................................................25 2.5.1.3 Monotonic and non-monotonic entailment and proof ......................................................................26 i 2.5.1.4 Circumscription for non-monotonic entailment and proof................................................................27 2.5.1.5 The frame problem...........................................................................................................................27 2.5.1.6 The ramification problem.................................................................................................................28 2.5.1.7 Inertia...............................................................................................................................................28 2.6 EVENT CALCULUS.................................................................................................................................28 2.6.1 Origins and general characteristics of Event Calculus............................................................28 2.6.1.1 Parsimony of representation.............................................................................................................29 2.6.1.2 Expressive flexibility.......................................................................................................................30 2.6.1.3 Elaboration tolerance........................................................................................................................30 2.6.2 Basic sorts and form.................................................................................................................30 2.6.2.1 Events (actions) ...............................................................................................................................30 2.6.2.2 Fluents .............................................................................................................................................30 2.6.2.3 Timepoints ......................................................................................................................................30 2.6.2.4 Predicates.........................................................................................................................................31 2.6.2.5 EC domain description.....................................................................................................................31 2.6.3 Representational capabilities of EC..........................................................................................32 2.6.3.1 Circumscription in EC......................................................................................................................32 2.6.3.2 Defeasible reasoning........................................................................................................................34 2.6.3.3 Handling contradictions...................................................................................................................34 2.6.3.4 Continuous change...........................................................................................................................35 2.6.3.5 Concurrency.....................................................................................................................................35 2.7 DISCRETE EVENT CALCULUS...................................................................................................................35 2.7.1 An example DEC sequence with equivalent EC sequence........................................................37 2.8 ALTERNATIVE FORMALISMS TO EVENT CALCULUS.......................................................................................39 2.8.1 Situation calculus......................................................................................................................39 2.8.2 Fluent calculus..........................................................................................................................40 2.8.3 PMON and TAL.........................................................................................................................41 2.8.4 K-IA classification of temporal logic formalisms.....................................................................42 2.8.5 General remarks........................................................................................................................42 2.9 EXISTING WORK ON TIME AND EVENT-BASED SEMANTIC WEB ONTOLOGIES.....................................................43 2.9.1 Time based Semantic Web ontologies ......................................................................................43 2.9.2 Event based Semantic Web ontologies......................................................................................44