The terminology is taken from logic and linguistics where subject-predicate or subject-predicate-object structures have very similar but definitely distinct meanings. For RDF, there is again a similar but distinct meaning that might be best described by example.
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2 More on triples 3 RDF implementations 4 See Also 5 External Links |
In the statement 'New York's postal abbreviation is NY', 'New York' would be the RDF subject. 'postal abbreviation' the RDF predicate and 'NY' the RDF object.
As far as encoding this into actual RDF triples, simply stating 'New York's postal abbreviation is NY' is not enough.
In a like manner, to say that the title of a page is "Tony Benn" and its publisher is "Wikipedia" would be two statements that would need more to them to be valid RDF statements. In the N-Triples form of RDF, these statements might look like:
Why this would be useful in any way is probably not apparent, but the crucial thing to understand is that while "the title of this page is 'Tony Benn'" might have meaning to a human, it means nothing to a computer. The purpose of RDF is to provide an encoding and interpretation mechanism so that resources can be described in a way that particular software can understand it, or better put: So that software can easier access data organized within structured parameters.
It should be understood that software has absolutely no common sense, and can only manipulate symbols within the rules given. It has no way of knowing what a "title" or a "Tony Benn" is, and can only manipulate symbols.
Both versions of the statements above are wordy because one requirement for a resource (as a subject or a predicate) is that they be unique. It is obvious why the subject resource should be unique. It says what exact resource is being described. The predicate needs to be unique so that the idea of Title or Publisher will not be ambiguous to software working with the description. If the software recognizes http://purl.org/dc/elements/1.1/title (a specific definition for a the concept of a title established by the Dublin Core Metadata Initiative), it will also know that this title is different from a land title or an honarary title or just the letters t-i-t-l-e put together.
This mechanism for describing resources is a major component for what is proposed by the W3C's Semantic Web activity to be the next evolutionary stage of the Web, enabling automated software to work with metadata so that users can deal with vast resources of the Web more efficiently and with more certainty.
By examples
Example 1: the postal abbreviation for New York
Example 2: a Wikipedia page about Tony Benn
<" class="external">http://en.wikipedia.org/Tony_Benn> <http://purl.org/dc/elements/1.1/title> "Tony Benn" .
and might be expressed in RDF/XML as:<" class="external">http://en.wikipedia.org/Tony_Benn> <http://purl.org/dc/elements/1.1/publisher> "Wikipedia" .
More on triples
RDF implementations
See Also
External Links