Ontological Indeterminacy and the Semantic Web Or Why the Controversy Over Same-Sex Marriage Poses A Fundamental Problem for Current Semantic Web Architecture

Ontological Indeterminacy and the Semantic Web Or Why the Controversy Over Same-Sex Marriage Poses A Fundamental Problem for Current Semantic Web Architecture

Allen Ginsberg (Consultant, USA)
DOI: 10.4018/978-1-60566-992-2.ch008
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The expected utility of the Semantic Web (SW) hinges upon the idea that machines, just like humans, can make and interpret statements about “real world” objects, properties, and relations. A cornerstone of this idea is the notion that Uniform Resource Identifiers (URIs) can be used to refer to entities existing independently of the web and to convey meanings. In this chapter, when a URI is used in this manner we will say that it is used declaratively, or that it is an R-URI. The key question is this: when an R-URI is used declaratively on the SW how is an agent, especially a non-human one, supposed to “understand” or “know” what it is intended to refer to or mean? Within the broad community of computational ontologists and SW practitioners there seems to be a widespread understanding that to provide a meaning/referent for an R-URI the responsible “web-presence” should return (or provide reference to) a formal ontology, or some set of formal “core assertions,” that can be used to “establish” the “denotation” of the R-URI. This view, which we will call the Ontology-Mediated (OM) view of SW reference/meaning, presupposes that terms can be given precise conditions for their applicability, and that the latter can be used to “pick out” the intended real world referent/meaning of terms. This chapter argues that the presuppositions of the OM view are incompatible with the requirement that SW terms/statements should be identical or analogous in meaning to corresponding natural language terms/statements. Natural language is a rule-governed activity, but the rules for using a term or uttering a statement are typically not fully determinate. This phenomenon is a consequence of Ontological Indeterminacy: the inescapable fact that two or more incompatible conceptual systems can often be applied to a domain of interest with equal empirical adequacy. This chapter presents a detailed “real world” example - based upon the currently controversial topic of same-sex marriage - and develops a use-case to buttress the claim that this phenomenon causes problems for the OM view. It seems, therefore, that SW developers/users are faced with a dilemma. If, on the one hand, formal semantic methods, like ontologies, are essential for “picking out” the meaning of SW terms, then those terms will not, in many cases, have the same meaning as their natural language counterparts. If, on the other hand, formal methods are not used to define SW terms, then how is it possible to provide them with meanings that can be interpreted by machines?In this chapter, we will see that this dilemma is based on the mistaken presupposition that the meanings of SW terms must always be determined by giving precise applicability conditions in order for the goals of the SW to be achieved. We show that this presupposition is bound up with the philosophical view that reference and meaning are a function of correspondence of language to reality. We will see that an alternative philosophical account, namely, a “meaning as use” point of view, can be the basis for an account of the meaning of SW terms that avoids the problems of the OM view. The key insight we draw from this account is that there is a distinction between the intention to use a term in some customary manner and the decision to adopt a formal theory that explains or explicates that usage. Formal methods provide a means of explicating the intended senses of SW terms so those senses can be processed by machines for use in certain applications. The intention to use a term according to a certain known natural language community usage, however, can be communicated and processed independently of the decision to accept a particular theory that explicates the intended sense. This account satisfies the goals of the SW and avoids the problems associated with the OM view.
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According to the World Wide Web Consortium’s (W3C) page on Semantic Web Activity (http://www.w3.org/2001/sw/), the Semantic Web (SW) is “about two things:”

… common formats for interchange of data… Also it is about language for recording how the data relates to real world objects. That allows a person, or a machine, to start off in one database, and then move through an unending set of databases which are connected not by wires but by being about the same thing. (Italics added.)

Though couched in terms of databases, this paragraph implies that the SW should make it possible for machines to interpret and make statements about “real world objects” that would be direct analogues to human-generated statements about the same things. In order for the formal language used by a machine to have the same kind of utility as a natural language used by a human, there must be a way for the reference/meaning of SW terms to be established. A key idea behind the SW is to use Uniform Resource Identifiers (URIs) to play this role by allowing them to be used to “identify” real world objects, properties, and relations. Although there has been some controversy concerning technical details (Clark 2002; Pepper 2003) it seems clear that schemes allowing URIs to be used to refer to things (while still allowing them to be used as addresses in URLs) is compatible with established protocols (Halpin and Thompson 2005; Pepper 2003; Ginsberg 2006).

All relevant accounts, beginning with IETF RFC 2396 (Berners-Lee et. a1. 1998), and up to and including recent web architecture work in W3C TAG (Lewis ed., 2007) and most recently (Booth 2009), accept and utilize the fundamental idea that URIs can be used to refer to (“identify”) things (“resources”), whether these be web pages, or objects, properties, relations, etc. existing independently of the web. Thus, in contrast to the Uniform ResourceLocators (URLs) of the original web, which can be thought of as being “addresses” for “locations” in a virtual space (the web), the SW requires that URIs also be used linguistically by agents in various contexts to make certain statements, just as words uttered by humans in various contexts can be used to do the same. In this chapter, when a URI is used in this manner we will say that it is used declaratively; we will also use the term “referential-URI” (R-URI for short) to designate this type of SW usage.

For a Uniform ResourceLocator (URL) there is no question about what it “refers to” or “means:” a URL is simply a kind of address, and one can only use it to attempt to retrieve whatever item (if any) is stored at the corresponding location. If it “identifies” anything, it identifies a virtual location, not the contents of the location; see (Ginsberg 2006) for a detailed discussion of this point. But when a URI is used declaratively on the SW, how is an agent, especially a non-human one, supposed to “understand” or “know” what its intended referent or meaning is? Given that R-URIs can be used as subjects, predicates, and objects in statements in RDF and other SW languages, it is vital that a SW agent be able to determine when they are being used to refer to the same entity or mean the same thing. While syntactic identity of R-URIs is a sufficient condition for resource-identity, it is not a necessary one. Syntactically different R-URIs can refer to the same resource. This issue has been the concern of recent research (Bouquet et. al., 2008). The concern of this chapter is, however, of a more fundamental, and admittedly, philosophical, nature. The key question we address here is the following: what exactly must be the case for it to be true to say that a machine has succeeded in using an R-URI to refer to some extra-web entity or to mean the same as some natural language term?

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