Foundations of Semantic Web Technologies

Ontologies and Rules 243

is so-called frames that provide a convenient syntax for specifying property

values of objects. The following example gives a simple fact, reminiscent of

the fact shown in Fig. 2.1 on page 20, encoded in a frame (assuming suitable

namespace declarations for book and crc):

book:uri[ex:publishedBy -> crc:uri]

Here, book:uri refers to an object for which attribute-value pairs are speci-

fied. When using RIF frames, we thus speak of objects, attributes, and values,

where RDF would use the terms subject, p redicate, and object. These slight

differences in naming should not be a cause for confusion; the next section

will confirm that