Man Cannot Live on Facts Alone
The semantic web’s fundamental construct for representing knowledge is called a triple, which is a highly intuitive and very natural way of expressing a fact. As an example, the sentence we’ve considered on many previous occasions—“Mr. Green killed Colonel Mustard in the study with the candlestick”—expressed as a triple might be something like (Mr. Green, killed, Colonel Mustard), where the constituent pieces of that triple refer to the subject, predicate, and object of the sentence. The Resource Description Framework (RDF) is the semantic web’s model for defining and enabling the exchange of triples. RDF is highly extensible in that while it provides a basic foundation for expressing knowledge, it can also be used to define specialized vocabularies called ontologies that provide precise semantics for modeling specific domains. More than a passing mention of specific semantic web technologies such as RDF, RDFa, RDF Schema, and OWL would be well out of scope here at the eleventh hour, but we will work through a high-level example that attempts to explain some of the hype around the semantic web in general.
Open-World Versus Closed-World Assumptions
One interesting difference between the way inference works in logic programming languages such as Prolog as opposed to in other technologies, such as the RDF stack, is whether they make open-world or closed-world assumptions about the universe. Logic programming languages such as Prolog and most traditional ...