RDF star "alternative baseline"

RDF-star alternative baseline
(VOTED 2024.11.14)

ABSTRACT SYNTAX

graph                 ::= triple*
triple                ::= tripleStructure
tripleStructure       ::= subject predicate object
subject               ::= NoLiteralTerm
predicate             ::= iri 
object                ::= term
NoLiteralTerm         ::= NoLiteralAtomicTerm | tripleTerm
NoLiteralAtomicTerm   ::= iri | BlankNode
tripleTerm            ::= tripleStructure
term                  ::= NoLiteralTerm | literal

Notes:

• RDF 1.1 syntax is the above without the tripleTerm category and its dependents.
• A term is denoted by r, a triple by t, and a graph by g.
• Given a triple structure s, we denote the subject, predicate, object of s as s.s, s.p, s.o, respectively.

SIMPLE SEMANTICS

An RDF simple interpretation I is a structure <IR, IP, IS, IL, IEXT, RE> consisting of:

1. A non-empty set IR of resources, called the domain or universe of I.
2. A set IP, called the set of properties of I.
3. A mapping IS from IRIs into IR ⋃ IP, called the interpretation of IRIs.
4. A partial mapping IL from literal into IR, called the interpretation of literals.
5. A mapping IEXT from IP into 2IR x IR, called the extension of properties.
6. ⏩ An injective function RE from IR x IP x IR into IR, called the denotation of triple terms. ⏪

A is a mapping from BlankNode to IR.

Given I and A, the function [I+A](.) is defined over terms, triples, and graphs as follows.

• [I+A](r) = IS(r)   if r is a iri
• [I+A](r) = IL(r)   if r is a literal
• ⏩ [I+A](r) = RE([I+A](r.s), [I+A](r.p), [I+A](r.o))   if r is a tripleTerm ⏪️
• [I+A](r) = A(r)   if r is a BlankNode

• [I+A](t) = TRUE   if and only if   <[I+A](t.s), [I+A](t.o)> ∈ IEXT([I+A](t.p))

• [I+A](g) = TRUE   if and only if   ∀ t ∈ g . [I+A](t) = TRUE

A simple interpretation I is a model of a graph g   if and only if   ∃ A . [I+A](g) = TRUE.

The set of all models of a graph g is called models(g).

Simple entailment: g ⊨ g'   if and only if   models(g) ⊆ models(g').

Notes:

• RDF 1.1 simple semantics is the above without the parts within ⏩...⏪ marks.

RDF SEMANTICS

RDF semantics restricts the function [I+A](.) with the following additional conditions:

⏩ [I+A](t) = TRUE   implies
          <[I+A](t.s), [I+A](rdf:TripleTerm)> ∈ IEXT([I+A](rdf:type))
          if t.s is a triple term ⏪️

⏩ [I+A](t) = TRUE   implies
          <[I+A](t.o), [I+A](rdf:TripleTerm)> ∈ IEXT([I+A](rdf:type))
          if t.o is a triple term ⏪️

⏩ [I+A](t) = TRUE   implies
          <[I+A](t.p), [I+A](rdf:ReificationProperty)> ∈ IEXT([I+A](rdf:type))
          if <[I+A](t.o), [I+A](rdf:TripleTerm)> ∈ IEXT([I+A](rdf:type)) ⏪️

⏩ [I+A](t) = TRUE   implies
          <[I+A](t.p), [I+A](rdf:InverseReificationProperty)> ∈ IEXT([I+A](rdf:type))
          if <[I+A](t.s), [I+A](rdf:TripleTerm)> ∈ IEXT([I+A](rdf:type)) ⏪️

A RDF interpretation I is a RDF model of a graph g   if and only if   ∃ A . [I+A](g) = TRUE.

The set of all RDF models of a graph g is called rdf-models(g).

RDF entailment: g ⊨ g'   if and only if   rdf-models(g) ⊆ rdf-models(g').

Notes:

• RDF 1.1 RDF semantics is the above without the parts within ⏩...⏪ marks.

Metamodelling: entailment patterns and axiomatic triples

	if S contains	then S RDF entails
reif1	sss aaa <<(xxx yyy zzz)>> .	aaa rdf:type rdf:ReificationProperty .
reif2	<<(xxx yyy zzz)>> aaa ooo .	aaa rdf:type rdf:InverseReificationProperty .
triple1	sss aaa <<(xxx yyy zzz)>> .	<<(xxx yyy zzz)>> rdf:type rdf:TripleTerm .
triple2	<<(xxx yyy zzz)>> aaa ooo .	<<(xxx yyy zzz)>> rdf:type rdf:TripleTerm .

RDF axiomatic triples
rdf:reifies rdf:type rdf:ReificationProperty .

BEST PRACTICE (informative) -- to be expanded...

The RDF 1.2 Concepts and Abstract Syntax document should be weakened or expanded, to reflect that we can use alternative reification properties:

RDF 1.2 Concepts and Abstract Syntax
Every triple with a triple term as its object SHOULD use http://www.w3.org/1999/02/22-rdf-syntax-ns#reifies (rdf:reifies) as its predicate. Every triple whose object is not a triple term SHOULD NOT use http://www.w3.org/1999/02/22-rdf-syntax-ns#reifies (rdf:reifies) as its predicate.

TURTLE SYNTAX (informative)

A triple term is represented in Turtle as follows:

<<( s p o )>>

The following temporary shortcut for a term (a triple term reifier) is added to Turtle, which can be used in arbitrary subject or object position:

<< s p o ~ e >>

which expands in Turtle, following the best practice, as follows:

<< s p o ~ e >> p1 o1 .   ==>   e rdf:reifies <<( s p o )>> .  e p1 o1 .
s1 p1 << s p o ~ e >> .   ==>   e rdf:reifies <<( s p o )>> .  s1 p1 e .