中文XML论坛--请教：rdf:about, rdf:resource, rdf:ID 有什么区别

贴子主题：请教：rdf:about, rdf:resource, rdf:ID 有什么区别

本主题类别: 经典问答 | RDF/RDFS

在RDF primer的第三章有解释：http://www.w3.org/TR/rdf-primer/
其中的对rdf:ID的解释：
An important difference from previous examples is that, in line 5, the rdf:Description element has an rdf:ID attribute instead of an rdf:about attribute. Using rdf:ID specifies a fragment identifier, given by the value of the rdf:ID attribute (item10245 in this case, which might be the catalog number assigned by example.com), as an abbreviation of the complete URIref of the resource being described. The fragment identifier item10245 will be interpreted relative to a base URI, in this case, the URI of the containing catalog document. The full URIref for the tent is formed by taking the base URI (of the catalog), and appending the character "#" (to indicate that what follows is a fragment identifier) and then item10245 to it, giving the absolute URIref http://www.example.com/2002/04/products#item10245.

The rdf:ID attribute is somewhat similar to the ID attribute in XML and HTML, in that it defines a name which must be unique relative to the current base URI (in this example, that of the catalog). In this case, the rdf:ID attribute appears to be assigning a name (item10245) to this particular kind of tent. Any other RDF/XML within this catalog could refer to the tent by using either the absolute URIref http://www.example.com/2002/04/products#item10245, or the relative URIref #item10245. The relative URIref would be understood as being a URIref defined relative to the base URIref of the catalog. Using a similar abbreviation, the URIref of the tent could also be given by specifying rdf:about="#item10245" in the catalog entry (i.e., by specifying the relative URIref directly) instead of rdf:ID="item10245" . As an abbreviation mechanism, the two forms are essentially synonyms: the full URIref formed by RDF/XML is the same in either case: http://www.example.com/2002/04/products#item10245. However, using rdf:ID provides an additional check when assigning a set of distinct names, since a given value of the rdf:ID attribute can only appear once relative to the same base URI (the catalog document, in this example). Using either form, example.com would be giving the URIref for the tent in a two-stage process, first assigning the URIref for the whole catalog, and then using a relative URIref in the description of the tent in the catalog to indicate the URIref that has been assigned to this particular kind of tent. Moreover, this use of a relative URIref can be thought of either as being an abbreviation for a full URIref that has been assigned to the tent independently of the RDF, or as being the assignment of the URIref to the tent within the catalog.


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