Semantics: Andy's proposal

RDF-star semantics: Andy's proposal

(DRAFT 2024.01.04)

ABSTRACT SYNTAX:

graph ::= (triple)*
triple ::= subject predicate object
subject ::= iri | BlankNode | tripleOccurrence
predicate ::= iri
object ::= term
term ::= iri | BlankNode | literal | tripleOccurrence
tripleOccurrence ::= (iri | BlankNode)? triple

Note:
Terms are denoted by r, triples by t, and graphs by g.
Given a triple occurrence r, we denote the identifier of r as r.id, and the subject, predicate, object of r as r.s, r.p, r.o, respectively.
Given a triple t, we denote the subject, predicate, object of t as t.s, t.p, t.o, respectively.
RDF 1.1 syntax is the above without the tripleOccurrence category.

SEMANTICS:

An RDF-star simple interpretation I is a structure <IR, IP, IS, IL, IEXT, IT, IO> 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. A binary relation IO over IR x (IR x IP x IR) , called the occurrence 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) = IL(r) if r is a literal
  
• [I+A](r) = IS(r) if r is a iri
  
• [I+A](r) = A(r) if r is a BlankNode
  
• [I+A](r) = [I+A](r.id) if r is a tripleOccurrence
  

• [I+A](t) = TRUE if and only if <[I+A](t.s),[I+A](t.o)> ∈ IEXT([I+A](t.p)) and
  • <[I+A](ts.id), <[I+A](ts.s),[I+A](ts.p),[I+A](ts.o)>> ∈ IO
    if t.s is a tripleOccurrence ts
  • <[I+A](to.id), <[I+A](to.s),[I+A](to.p),[I+A](to.o)>> ∈ IO
    if t.o is a tripleOccurrence to

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

An interpretation I is called a model for g if there exists A such that [I+A](g) = TRUE.

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

Note:
RDF 1.1 semantics is the above without the IO binary relation in the interpretation.
A review of the standard semantics of RDF 1.0: semantics of RDF.pdf.

EXAMPLE CASES IN CONCRETE SYNTAX:

<< :wed-1 | :liz :spouse :richard >>
 :start 1964 ;
 :end 1974 .
<< :wed-2 | :liz :spouse :richard >>
 :start 1975 ;
 :end 1976 .

The above entails:

<< [] | :liz :spouse _:x >>
 :start 1964.

Shortcuts in concrete syntax:

• Triple term shortcut: << :s :p :o >> ➡️
  << [] | :s :p :o >>
• Annotation shortcut: :s :p :o {| :id | :p1 o1; :p2 o2 |} . ➡️
  << :id | :s :p :o >> :p1 o1; :p2 o2 .
:s :p :o .