Context Slices: Representing Contexts in OWL http://ontologydesignpatterns.org/wiki/Submissions:Context_Slices Chris Welty IBM Watson Research Hawthorne, NY 12540, USA cawelty@gmail.com ABSTRACT This allows us to represent ceoOf as a binary relation, which This ontology pattern can be used to represent and reason about seems more natural, and it allows us to use the expressivity of contextualized statements using standard OWL dialects. The OWL in more ways. We can say of the ceoOf relation that it has simple idea is to bundle the notion of context into certain nodes in an inverse, hasCeo. We can express cardinality, e.g., a company the graph, rather than the more typical treatment of contexts as a may have only one CEO within a context. We can say that a property of the statements themselves. relation is transitive or symmetric. We can express relation taxonomies in the usual way. Keywords While clearly OWL does not support RDF reification, and so none Semantic Web, OWL, RDF, Contexts. of this is possible if statement reification is used. As mentioned above a more standard way of representing this kind of information (including time, belief, knowledge, etc.) is to create 1. INTRODUCTION an OWL class that represents the relation holding, with properties Most information on the web is contextualized somehow, for for the arguments. This approach makes it possible to express example information may be believed by a person or organization, global but not local range and domain constraints, global but not it may hold only for some time period, it may have been local cardinality, and symmetry. reported/observed by an individual, etc. There are myriad Note that the ContextualProjection class should be considered proposals and logics for context, but none are standards and few disjoint with any of the classes in an ontology that have have even prototype implementations. projections. In RDF and other binary relation languages (like object oriented languages and description logics), one typical way to represent that a binary relation holds in some context is to "reify" the relation-holding in the context as an object with a binary relation between the obtainment and each the two relation arguments and a third binary relation between the obtainment and an object representing the context itself. The downside to this approach is the expressive ability of the language to describe the binary relation, especially in the case of description logics, is lost. One can of course use RDF reification, however this is not supported in OWL, either. The motivation for context slices is to provide a logical pattern for encoding context information in standard RDF graphs that allows some of the expressiveness of OWL to be used in describing the relations that hold in contexts. This is a generalization of the four dimensional ontology for fluents published in [1]. 2. PATTERN DESCRIPTION The idea of the context slices pattern is, rather than reifying the Figure 1: Graphical illustration of an example using the pattern. statement itself, to create a projection of the ''relation arguments'' in each context for which some binary relation holds between them. Take for example the statement "Chris believes Sam is CEO of 3. IMPLEMENTATION IBM". Say we already have nodes in some graph representing In OWL functional syntax: Sam, Chris and IBM. We create, as shown in Figure 1, the context c1 corresponding to Chris' belief, and two nodes Ontology( representing Chris' belief about Sam and Chris' belief about IBM Annotation(owl:versionInfo "1.0"@en) (shown as Sam@c1 and IBM@c1). Annotation(rdfs:label "Context slices ontology logical pattern"@en) ObjectPropertyDomain(cs:hasContext Declaration(Class(cs:Context)) cs:ContextualProjection) DisjointClasses(cs:Context cs:ContextualProjection) Declaration(ObjectProperty(cs:projectionOf)) Declaration(Class(cs:ContextualProjection)) FunctionalObjectProperty(cs:projectionOf) SubClassOf(cs:ContextualProjection ObjectPropertyDomain(cs:projectionOf ObjectAllValuesFrom(cs:hasContext cs:Context)) cs:ContextualProjection)) SubClassOf(cs:ContextualProjection ObjectExactCardinality(1 cs:hasContext)) SubClassOf(cs:ContextualProjection 4. REFERENCES ObjectExactCardinality(1 cs:projectionOf)) [1] Welty, Chris and Richard E. Fikes. 2006. A Reusable DisjointClasses(cs:ContextualProjection cs:Context) Ontology for Fluents in OWL. In Bennet and Fellbaum, eds., Declaration(ObjectProperty(cs:contextualProperty)) Proceedings of the Fourth International Conference on ObjectPropertyDomain(cs:contextualProperty Formal Ontology in Information Systems. IOS Press. See cs:ContextualProjection) http://www.booksonline.iospress.nl/Content/View.aspx?piid ObjectPropertyRange(cs:contextualProperty =2209. cs:ContextualProjection) Declaration(ObjectProperty(cs:hasContext)) FunctionalObjectProperty(cs:hasContext)