【RDF】：Reification（RDF的边上能搞属性吗？）

目录
1. 背景
2. RDF Reification 有什么用？
3. RDF reification 词汇表
4. RDF Reification 详解

1. 背景

问：下图这种结构（边上有属性），怎么用 RDF 搞？

答：不能直接搞，但是可以间接搞

RDF Reification 是其中一种解决方案

2. RDF Reification 有什么用？

The intended meaning of this vocabulary is to allow an RDF graph to act as metadata describing other RDF triples.

PREFIX : <http://example.org/ontology#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX person: <http://example.org/data/person/>
PREFIX statement: <http://example.org/data/statement/>

person:Bob :loves person:Mary.

statement:1 a rdf:Statement;
    rdf:subject person:Bob;
    rdf:predicate :loves;
    rdf:object person:Mary;
    :reason <http://loveletters.com/123>.

3. RDF reification 词汇表

• rdf:Statement
• rdf:subject
• rdf:predicate
• rdf:object

4. RDF Reification 详解

Consider an example graph containing a single triple:

ex:a ex:b ex:c .

and suppose that IRI ex:graph1 is used to identify this graph. Exactly how this identification is achieved is external to the RDF model, but it might be by the IRI resolving to a concrete syntax document describing the graph, or by the IRI being the associated name of a named graph in a dataset. Assuming that the IRI can be used to refer to the triple, then the reification vocabulary allows us to describe the first graph in another graph:

ex:graph1 rdf:type rdf:Statement .
ex:graph1 rdf:subject ex:a .
ex:graph1 rdf:predicate ex:b .
ex:graph1 rdf:object ex:c .

The second graph is called a reification of the triple in the first graph. Reification is not a form of quotation. Rather, the reification describes the relationship between a token of a triple and the resources that the triple refers to. The value of the rdf:subject property is not the subject IRI itself but the thing it denotes, and similarly for rdf:predicate and rdf:object. For example, if the referent of ex:a is Mount Everest, then the subject of the reified triple is also the mountain, not the IRI which refers to it. Reifications can be written with a blank node as subject, or with an IRI subject which does not identify any concrete realization of a triple, in both of which cases they simply assert the existence of the described triple. The subject of a reification is intended to refer to a concrete realization of an RDF triple, such as a document in a surface syntax, rather than a triple considered as an abstract object. This supports use cases where properties such as dates of composition or provenance information are applied to the reified triple, which are meaningful only when thought of as referring to a particular instance or token of a triple. A reification of a triple does not entail the triple, and is not entailed by it. The reification only says that the triple token exists and what it is about, not that it is true, so it does not entail the triple. On the other hand, asserting a triple does not automatically imply that any triple tokens exist in the universe being described by the triple. For example, the triple might be part of an ontology describing animals, which could be satisfied by an interpretation in which the universe contained only animals, and in which a reification of it was therefore false. Since the relation between triples and reifications of triples in any RDF graph or graphs need not be one-to-one, asserting a property about some entity described by a reification need not entail that the same property holds of another such entity, even if it has the same components. For example,

_:xxx rdf:type rdf:Statement .
_:xxx rdf:subject ex:subject .
_:xxx rdf:predicate ex:predicate .
_:xxx rdf:object ex:object .

_:yyy rdf:type rdf:Statement .
_:yyy rdf:subject ex:subject .
_:yyy rdf:predicate ex:predicate .
_:yyy rdf:object ex:object .

_:xxx ex:property ex:foo .

does not entail

_:yyy ex:property ex:foo .

参考：

RDF reification： https://www.w3.org/TR/rdf11-mt/#reification