Add support for RDF 1.2 Triple Terms and deprecation notices for RDF-…

…star quoted triples.

Note all RDF 1.2 and RDF-star support remains experimental and may be changed or removed in a future minor or patch version.

README.md

@@ -265,9 +265,15 @@ A separate [SPARQL][SPARQL doc] gem builds on basic BGP support to provide full
     foaf[:name]   #=> RDF::URI("http://xmlns.com/foaf/0.1/name")
     foaf['mbox']  #=> RDF::URI("http://xmlns.com/foaf/0.1/mbox")
 
+## RDF-star CG
+
+[RDF.rb][] includes provisional support for [RDF-star][] with an N-Triples/N-Quads syntax for quoted triples in the _subject_ or _object_ position.
+
+Support for RDF-star quoted triples is now deprecated, use RDF 1.2 triple terms instead.
+
 ## RDF 1.2
 
-[RDF.rb][] includes provisional support for [RDF 1.2][] with an N-Triples/N-Quads syntax for quoted triples in the _subject_ or _object_ position.
+[RDF.rb][] includes provisional support for [RDF 1.2][] with an N-Triples/N-Quads syntax for triple terms in the _object_ position.
 [RDF.rb][] includes provisional support for [RDF 1.2][] directional language-tagged strings, which are literals of type `rdf:dirLangString` having both a `language` and `direction`.
 
 Internally, an `RDF::Statement` is treated as another resource, along with `RDF::URI` and `RDF::Node`, which allows an `RDF::Statement` to have a `#subject` or `#object` which is also an `RDF::Statement`.
@@ -501,6 +507,7 @@ see <https://unlicense.org/> or the accompanying {file:UNLICENSE} file.
 [SPARQL doc]:       https://ruby-rdf.github.io/sparql
 [RDF 1.0]:          https://www.w3.org/TR/2004/REC-rdf-concepts-20040210/
 [RDF 1.1]:          https://www.w3.org/TR/rdf11-concepts/
+[RDF-star]:         https://www.w3.org/2021/12/rdf-star.html
 [RDF 1.2]:          https://www.w3.org/TR/rdf12-concepts/
 [SPARQL 1.1]:       https://www.w3.org/TR/sparql11-query/
 [RDF.rb]:           https://ruby-rdf.github.io/

etc/n-triples.ebnf

@@ -2,8 +2,9 @@ ntriplesDoc       ::= triple? (EOL triple)* EOL?
 triple            ::= subject predicate object '.'
 subject           ::= IRIREF | BLANK_NODE_LABEL | quotedTriple
 predicate         ::= IRIREF
-object            ::= IRIREF | BLANK_NODE_LABEL | literal | quotedTriple
+object            ::= IRIREF | BLANK_NODE_LABEL | literal | tripleTerm | quotedTriple
 literal           ::= STRING_LITERAL_QUOTE ('^^' IRIREF | LANG_DIR )?
+tripleTerm        ::= '<<' subject predicate object '>>'
 quotedTriple      ::= '<<' subject predicate object '>>'
 
 @terminals

lib/rdf/mixin/enumerable.rb

@@ -83,7 +83,8 @@ def to_a
     #   * `:literal_equality' preserves [term-equality](https://www.w3.org/TR/rdf11-concepts/#dfn-literal-term-equality) for literals. Literals are equal only if their lexical values and datatypes are equal, character by character. Literals may be "inlined" to value-space for efficiency only if `:literal_equality` is `false`.
     #   * `:validity` allows a concrete Enumerable implementation to indicate that it does or does not support valididty checking. By default implementations are assumed to support validity checking.
     #   * `:skolemize` supports [Skolemization](https://www.w3.org/wiki/BnodeSkolemization) of an `Enumerable`. Implementations supporting this feature must implement a `#skolemize` method, taking a base URI used for minting URIs for BNodes as stable identifiers and a `#deskolemize` method, also taking a base URI used for turning URIs having that prefix back into the same BNodes which were originally skolemized.
-    #   * `:quoted_triples` supports RDF 1.2 quoted triples.
+    #   * `:rdf_full` supports RDF 1.2 Full profile, including support for embedded Triple Terms.
+    #   * `:quoted_triples` supports RDF-star quoted triples.
     #   * `:base_direction` supports RDF 1.2 directional language-tagged strings.
     #
     # @param  [Symbol, #to_sym] feature

lib/rdf/mixin/writable.rb

@@ -127,7 +127,8 @@ def insert_graph(graph)
     def insert_statements(statements)
       each = statements.respond_to?(:each_statement) ? :each_statement : :each
       statements.__send__(each) do |statement|
-        if statement.embedded? && respond_to?(:supports?) && !supports?(:quoted_triples)
+        # FIXME: quoted triples are now deprecated
+        if statement.embedded? && respond_to?(:supports?) && !(supports?(:quoted_triples) || supports?(:rdf_full))
           raise ArgumentError, "Writable does not support quoted triples"
         end
         if statement.object && statement.object.literal? && statement.object.direction? && respond_to?(:supports?) && !supports?(:base_direction)

lib/rdf/model/dataset.rb

@@ -104,7 +104,8 @@ def isolation_level
     # @private
     # @see RDF::Enumerable#supports?
     def supports?(feature)
-      return true if %i(graph_name quoted_triples).include?(feature)
+      # FIXME: quoted triples are now deprecated
+      return true if %i(graph_name quoted_triples rdf_full).include?(feature)
       super
     end
 

lib/rdf/model/graph.rb

@@ -305,8 +305,9 @@ def query_pattern(pattern, **options, &block)
     # @private
     # @see RDF::Mutable#insert
     def insert_statement(statement)
-      if statement.embedded? && !@data.supports?(:quoted_triples)
-        raise ArgumentError, "Graph does not support quoted triples"
+      # FIXME: quoted triples are now deprecated
+      if statement.embedded? && !(@data.supports?(:quoted_triples) || @data.supports?(:rdf_full))
+        raise ArgumentError, "Graph does not support the RDF Full profile"
       end
       if statement.object && statement.object.literal? && statement.object.direction? &&  !@data.supports?(:base_direction)
         raise ArgumentError, "Graph does not support directional languaged-tagged strings"

lib/rdf/model/statement.rb

@@ -71,7 +71,8 @@ def self.from(statement, graph_name: nil, **options)
     #   @option options [RDF::Term]  :graph_name   (nil)
     #     Note, in RDF 1.1, a graph name MUST be an {Resource}.
     #   @option options [Boolean] :inferred used as a marker to record that this statement was inferred based on semantic relationships (T-Box).
-    #   @option options [Boolean] :quoted used as a marker to record that this statement quoted and appears as the subject or object of another RDF::Statement.
+    #   @option options [Boolean] :tripleTerm used as a marker to record that this statement appears as the object of another RDF::Statement.
+    #   @option options [Boolean] :quoted used as a marker to record that this statement quoted and appears as the subject or object of another RDF::Statement (deprecated).
     #   @return [RDF::Statement]
     #
     # @overload initialize(subject, predicate, object, **options)
@@ -84,7 +85,8 @@ def self.from(statement, graph_name: nil, **options)
     #   @option options [RDF::Term]  :graph_name   (nil)
     #     Note, in RDF 1.1, a graph name MUST be an {Resource}.
     #   @option options [Boolean] :inferred used as a marker to record that this statement was inferred based on semantic relationships (T-Box).
-    #   @option options [Boolean] :quoted used as a marker to record that this statement quoted and appears as the subject or object of another RDF::Statement.
+    #   @option options [Boolean] :tripleTerm used as a marker to record that this statement appears as the object of another RDF::Statement.
+    #   @option options [Boolean] :quoted used as a marker to record that this statement quoted and appears as the subject or object of another RDF::Statement (deprecated).
     #   @return [RDF::Statement]
     def initialize(subject = nil, predicate = nil, object = nil, options = {})
       if subject.is_a?(Hash)
@@ -211,6 +213,13 @@ def asserted?
 
     ##
     # @return [Boolean]
+    def tripleTerm?
+      !!@options[:tripleTerm]
+    end
+
+    ##
+    # @return [Boolean]
+    # @deprecated Quoted triples are now deprecated
     def quoted?
       !!@options[:quoted]
     end

lib/rdf/nquads.rb

@@ -71,9 +71,10 @@ def read_triple
 
           begin
             unless blank? || read_comment
+              # FIXME: quoted triples are now deprecated
               subject   = read_uriref || read_node || read_quotedTriple || fail_subject
               predicate = read_uriref(intern: true) || fail_predicate
-              object    = read_uriref || read_node || read_literal || read_quotedTriple || fail_object
+              object    = read_uriref || read_node || read_literal || read_tripleTerm || read_quotedTriple || fail_object
               graph_name    = read_uriref || read_node
               if validate? && !read_eos
                 log_error("Expected end of statement (found: #{current_line.inspect})", lineno: lineno, exception: RDF::ReaderError)

lib/rdf/ntriples.rb

@@ -15,7 +15,11 @@ module RDF
   #
   #     <https://rubygems.org/gems/rdf> <http://purl.org/dc/terms/title> "rdf" .
   #
-  # ## Quoted Triples
+  # ## Triple terms
+  #
+  # Supports statements as resources using `<<(s p o)>>`.
+
+  # ## Quoted Triples (Deprecated)
   #
   # Supports statements as resources using `<<s p o>>`.
   #

lib/rdf/ntriples/reader.rb

@@ -70,8 +70,11 @@ class Reader < RDF::Reader
     LANG_DIR             = /@([a-zA-Z]+(?:-[a-zA-Z0-9]+)*(?:--[a-zA-Z]+)?)/.freeze
     STRING_LITERAL_QUOTE = /"((?:[^\"\\\n\r]|#{ECHAR}|#{UCHAR})*)"/.freeze
 
-    ST_START              = /^<</.freeze
-    ST_END                = /^\s*>>/.freeze
+    TT_START              = /^<<\(/.freeze
+    TT_END                = /^\s*\)>>/.freeze
+
+    QT_START              = /^<</.freeze
+    QT_END                = /^\s*>>/.freeze
 
     # @see http://www.w3.org/TR/rdf-testcases/#ntrip_grammar
     COMMENT               = /^#\s*(.*)$/.freeze
@@ -208,7 +211,7 @@ def read_value
       begin
         read_statement
       rescue RDF::ReaderError
-        value = read_uriref || read_node || read_literal || read_quotedTriple
+        value = read_uriref || read_node || read_literal || read_tripleTerm || read_quotedTriple
         log_recover
         value
       end
@@ -226,7 +229,7 @@ def read_triple
           unless blank? || read_comment
             subject   = read_uriref || read_node || read_quotedTriple || fail_subject
             predicate = read_uriref(intern: true) || fail_predicate
-            object    = read_uriref || read_node || read_literal || read_quotedTriple || fail_object
+            object    = read_uriref || read_node || read_literal || read_tripleTerm || read_quotedTriple || fail_object
 
             if validate? && !read_eos
               log_error("Expected end of statement (found: #{current_line.inspect})", lineno: lineno, exception: RDF::ReaderError)
@@ -242,12 +245,29 @@ def read_triple
 
     ##
     # @return [RDF::Statement]
+    def read_tripleTerm
+      if @options[:rdfstar] && match(TT_START)
+        subject   = read_uriref || read_node || fail_subject
+        predicate = read_uriref(intern: true) || fail_predicate
+        object    = read_uriref || read_node || read_literal || read_tripleTerm || fail_object
+        if !match(TT_END)
+          log_error("Expected end of statement (found: #{current_line.inspect})", lineno: lineno, exception: RDF::ReaderError)
+        end
+        RDF::Statement.new(subject, predicate, object, tripleTerm: true)
+      end
+    end
+
+    ##
+    # @return [RDF::Statement]
+    # @deprecated Quoted triples are now deprecated
     def read_quotedTriple
-      if @options[:rdfstar] && match(ST_START)
+      if @options[:rdfstar] && match(QT_START)
+        warn "[DEPRECATION] RDF-star quoted triples are deprecated and will be removed in a future version.\n" +
+             "Called from #{Gem.location_of_caller.join(':')}"
         subject   = read_uriref || read_node || read_quotedTriple || fail_subject
         predicate = read_uriref(intern: true) || fail_predicate
         object    = read_uriref || read_node || read_literal || read_quotedTriple || fail_object
-        if !match(ST_END)
+        if !match(QT_END)
           log_error("Expected end of statement (found: #{current_line.inspect})", lineno: lineno, exception: RDF::ReaderError)
         end
         RDF::Statement.new(subject, predicate, object, quoted: true)

lib/rdf/ntriples/writer.rb

@@ -223,15 +223,28 @@ def format_statement(statement, **options)
       format_triple(*statement.to_triple, **options)
     end
 
+    ##
+    # Returns the N-Triples representation of an RDF 1.2 triple term.
+    #
+    # @param  [RDF::Statement] statement
+    # @param  [Hash{Symbol => Object}] options ({})
+    # @return [String]
+    def format_tripleTerm(statement, **options)
+      "<<(%s %s %s)>>" % statement.to_a.map { |value| format_term(value, **options) }
+    end
+
     ##
     # Returns the N-Triples representation of an RDF-star quoted triple.
     #
     # @param  [RDF::Statement] statement
     # @param  [Hash{Symbol => Object}] options ({})
     # @return [String]
+    # @deprecated Quoted triples are now deprecated
     def format_quotedTriple(statement, **options)
+      # FIXME: quoted triples are now deprecated
       "<<%s %s %s>>" % statement.to_a.map { |value| format_term(value, **options) }
     end
+
     ##
     # Returns the N-Triples representation of a triple.
     #

lib/rdf/repository.rb

@@ -182,6 +182,8 @@ def supports?(feature)
       when :validity         then @options.fetch(:with_validity, true)
       when :literal_equality then true
       when :atomic_write     then false
+      when :rdf_full         then false
+      # FIXME: quoted triples are now deprecated
       when :quoted_triples   then false
       when :base_direction   then false
       when :snapshots        then false
@@ -270,6 +272,7 @@ def supports?(feature)
         when :validity         then @options.fetch(:with_validity, true)
         when :literal_equality then true
         when :atomic_write     then true
+        when :rdf_full         then true
         when :quoted_triples   then true
         when :base_direction   then true
         when :snapshots        then true

lib/rdf/writer.rb

@@ -518,7 +518,8 @@ def format_term(term, **options)
         when RDF::Literal   then format_literal(term, **options)
         when RDF::URI       then format_uri(term, **options)
         when RDF::Node      then format_node(term, **options)
-        when RDF::Statement then format_quotedTriple(term, **options)
+        # FIXME: quoted triples are now deprecated
+        when RDF::Statement then term.tripleTerm? ? format_tripleTerm(term, **options) : format_quotedTriple(term, **options)
         else nil
       end
     end
@@ -566,7 +567,7 @@ def format_list(value, **options)
     end
 
     ##
-    # Formats a referenced triple.
+    # Formats a referenced triple term.
     #
     # @example
     #     <<<s> <p> <o>>> <p> <o> .
@@ -576,8 +577,24 @@ def format_list(value, **options)
     # @return [String]
     # @raise  [NotImplementedError] unless implemented in subclass
     # @abstract
+    def format_tripleTerm(value, **options)
+      raise NotImplementedError.new("#{self.class}#format_tripleTerm") # override in subclasses
+    end
+
+    ##
+    # Formats a referenced quoted triple.
+    #
+    # @example
+    #     <<<s> <p> <o>>> <p> <o> .
+    #
+    # @param  [RDF::Statement] value
+    # @param  [Hash{Symbol => Object}] options = ({})
+    # @return [String]
+    # @raise  [NotImplementedError] unless implemented in subclass
+    # @abstract
+    # @deprecated Quoted Triples are now deprecated in favor of Triple Terms
     def format_quotedTriple(value, **options)
-      raise NotImplementedError.new("#{self.class}#format_statement") # override in subclasses
+      raise NotImplementedError.new("#{self.class}#format_quotedTriple") # override in subclasses
     end
 
   protected

spec/model_statement_spec.rb

@@ -75,7 +75,8 @@
     it {is_expected.to have_object}
     its(:object) {is_expected.not_to be_nil}
     it {is_expected.to be_asserted}
-    it {is_expected.not_to be_quoted}
+    it {is_expected.not_to be_tripleTerm}
+    it {is_expected.not_to be_quoted} # FIXME: quoted triples are deprecated
     it {is_expected.to be_statement}
     it {is_expected.not_to be_inferred}
     its(:terms) {is_expected.to include(s, p, o)}
@@ -210,6 +211,12 @@
     it {is_expected.to be_inferred}
   end
 
+  context "when marked as tripleTerm" do
+    subject {RDF::Statement.new(RDF::Node.new, p, o, tripleTerm: true)}
+    it {is_expected.to be_tripleTerm}
+  end
+
+  # FIXME: quoted triples are deprecated
   context "when marked as quoted" do
     subject {RDF::Statement.new(RDF::Node.new, p, o, quoted: true)}
     it {is_expected.to be_quoted}

spec/nquads_spec.rb

@@ -180,7 +180,8 @@
     end
   end
 
-  context "RDF-star" do
+  # FIXME: quoted triples are deprecated
+  context "quoted triples" do
     statements = {
       "subject-iii": '<<<http://example/s1> <http://example/p1> <http://example/o1>>> <http://example/p> <http://example/o> <http://example/g> .',
       "subject-iib": '<<<http://example/s1> <http://example/p1> _:o1>> <http://example/p> <http://example/o> <http://example/g> .',
@@ -205,7 +206,13 @@
 
     statements.each do |name, st|
       context name do
-        let(:graph) {RDF::Graph.new << RDF::NQuads::Reader.new(st, rdfstar: true)}
+        let(:graph) do
+          g = RDF::Graph.new
+          expect do
+            g << RDF::NQuads::Reader.new(st, rdfstar: true)
+          end.to write('[DEPRECATION]').to(:error)
+          g
+        end
 
         it "creates two statements" do
           expect(graph.count).to eql(1)