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Nesting Graphs via Transclusion

Transclusion is the mechanism driving graph nesting. It imports a graph into another graph. Transclusion is transitive: if the transcluded graph contains further transclusion directives, those are executed (i.e. transcluded) as well. A TriG example without extra syntactic support illustrates its application:

:NG_2 nng:transcludes :NG_1 .
:NG_1 { :a :b :c }
:NG_2 { :d :e :f }

The location of the transclusion statement does matter. In the preceding example the transclusion directive is not visible, and therefore not executed, when inspecting :NG_2 in isolation.

In the following example :NG_2 always includes :NG_1:

:NG_1 { :a :b :c }
:NG_2 { 
    :d :e :f . 
    :NG_2 nng:transcludes :NG_1 . 
}

Syntactic Sugar

Explicitly stating a transclusion via an nng:transcludes relation is not necessary when the NNG syntax is used, like in the following example:

:NG_2 { 
    :d :e :f . 
    :NG_1 { :a :b :c }
}

Inheritance of Annotations

Annotations are inherited if they target the whole graph. That is the case if they use:

Annotations on individual nodes - subject, predicate, object or triples - in a nested graph are not inherited by graphs nested as such nodes.

Transclusion vs Inclusion vs owl:imports

The differences to the inclusion mechanism is that

  • inclusion is defined on graph literals, whereas transclusion is defined on graph sources, and
  • inclusion is not transitive, but transclusion is.

There is little, if any, difference to owl:imports, but it seems prudent to define a new property for a task so central to this proposal.

Vocabulary

The nng:transcludes property is defined as:

# VOCABULARY

nng:transcludes a rdf:Property,
    rdfs:subPropertyOf owl:imports ;
    rdfs:domain nng:NamedGraph ;
    rdfs:range nng:NestedGraph ;
    rdfs:comment "Includes a graph source into another graph source. Transclusion is transitive: if the transcluded source contains further transclusion directives, those are executed as well." .

Note that the nesting graph is of type nng:NamedGraph, meaning that its semantics are not specified. This is meant to ensure backwards compatibility with RDF 1.1 named graphs.