3.2 The Semantic Web Information Model: The ...
3.2 The Semantic Web Information Model: The Resource
Description Framework (RDF)
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On the Semantic Web, information is represented as a set of assertions called statements made up of three parts: subject, predicate, and object. Because of these three parts, statements are also sometimes referred to as triples. |
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Assertions of this form naturally form a directed graph, with subjects and objects of each statement as nodes, and predicates as edges. This is the data model used by the Semantic Web, and it is formalized in the language called the Resource Description Framework (RDF). |
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Nodes: Resources and Literals |
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The nodes of an RDF graph are the subjects and the objects of the statements that make up the graph. There are two kinds of nodes: resources and literals. Literals represent concrete data values like numbers or strings and cannot be the subjects of statements, only the objects. Resources, in contrast, represent everything else, and they can be either subjects or objects. |
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Edges: Predicates |
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Predicates, also called properties, represent the connections between resources; predicates are themselves resources, however, and RDF statements can be made about predicates just as they can about any other resources. One special type of predicate defined byRDF is type. The rdf:typepredicate is used to group resources together. |