new doc that introduces properties related to well-formedness #117
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| * If *s* is an IRI or a blank node, *p* is an IRI, and *o* is an IRI, a blank node, or a literal, then (*s*, *p*, *o*) is a triple term. | ||
| * If *s* is an IRI or a blank node, *p* is an IRI, and *o* is a triple term, then (*s*, *p*, *o*) is a triple term. | ||
| * If *s* is a triple term, *p* is an IRI, and *o* is an IRI, a blank node, or a literal, then (*s*, *p*, *o*) is a triple term. |
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Is there a reason this not also true?
* If *s* is a triple term, *p* is an IRI, and *o* is an IRI, a blank node, a literal, or a triple term, then (*s*, *p*, *o*) is a triple term.
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| **Definition:** An **RDF triple** (usually called "triple") is a 3-tuple (*s*, *p*, *o*) where: | ||
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| * *s* is an IRI, a blank node, or a triple term, |
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The abstract data model should not be extended to allow triple terms in the subject position.
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It is good to have a document that enumerates all the possible syntactic properties.
The document discusses triple-terms in section Triple-Term-Placement Well-Formedness.
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The abstract data model should not be extended to allow triple terms in the subject position.
For this document, I thought it is useful to go back and use the least restrictive model as the basis, to then define the different possible syntactic restrictions on top of it. I admit, however, that the notion of triple-term-placement well-formedness that I had defined is mixing two separate things; namely the question whether triple terms can be used in the subject and the question whether a triple term in the object requires the predicate to be rdf:reifies. So, in the spirit of trying to capture all possible restrictions separate from one another, I have changed this part of the document by splitting the earlier-defined notion of triple-term-placement well-formedness into two separate new notions: triple-term-subject well-formedness and triple-term-object well-formedness.
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If we have have general purpose reification, it's odd to restrict the usage of triple terms in "helper" ways. Maybe we need "advisories", which is weaker than well-formedness ("implementations SHOULD warn and SHOULD accept").
Even then:
<<( :s :p :o )>> rdf:type rdf:Triple .
<<( :s :p :o )>> skos:prefLabel "Appearance" .
Having these definitions is useful to bring out all the cases:
:myProperty rdfs:subPropertyOf rdf:reifies .
:r :myProperty <<( :s :p :o )>> .
It occurs to me that the notion of well-formedness that the group strives for has more facets than just the decision of whether
rdf:reifiesis many-to-many or many-to-one, and I think it would be useful for us to be able to discuss and to decide about these facets independent of one another. Therefore, I have created a document in which I define different syntactic properties that an RDF graph with triple terms may possess, where each of these properties corresponds to one of the facets that I see. The important point is that these properties are completely orthogonal, and we can decide which of them we include as the properties required for well-formedness.