%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% The following collection of Xcerpt rules     %%
%% parses and normalizes RDF/XML files into     %%
%% straight triples                             %%
%% -------------------------------------------- %%
%% For more details see Oliver Bolzer, "Towards 
%% Data-Integration on the Semantic Web: Querying 
%% RDF with Xcerpt". Diploma Thesis, 2004
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Top-Level Subjects
CONSTRUCT
  RDFXML-SUBJECT[ var ORIGIN, var SUB ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  RDF-FILE[
    var ORIGIN,
    rdf:RDF{{
      var SUB
    }}
  ]
END

% Recursion, subject-predicate-object nesting
CONSTRUCT
  RDFXML-SUBJECT[ var ORIGIN, var OBJECT ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[
    RDF-FILE[
      var ORIGIN,
      rdf:RDF{{ desc identity var IDENT var OBJECT as /.*/:/.*/{{}} }}
    ],
    RDFXML-SUBJECT[ var ORIGIN, 
      /.*/:/.*/{{     % subject
        /.*/:/.*/{{   % predicate with child as object
          without attributes{{ rdf:parseType{ "Literal" } }},
          without attributes{{ rdf:parseType{ "Resource"} }},
          identity var IDENT var OBJECT
        }}
      }}
    ]
  ]
END

% regular URI reference
CONSTRUCT
  RDFXML-NODE[ var ORIGIN, var NODE, var URI:uri{} ]
FROM
    ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

    RDFXML-SUBJECT[ 
      var ORIGIN,
      var NODE as /.*/:/.*/{{
        attributes{{ rdf:about{ var URI } }}
      }}
    ]
END

% relative URI reference
CONSTRUCT
  RDFXML-NODE[ var ORIGIN, var NODE, &join( var ORIGIN, "#", var ID):uri{} ]
FROM
    ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

    RDFXML-SUBJECT[ 
      var ORIGIN,
      var NODE as /.*/:/.*/{{
        attributes{{ rdf:ID{ var ID } }}
      }}
    ]
END

% blank node with explicit identifier
CONSTRUCT
  RDFXML-NODE[ var ORIGIN, var NODE, var NODEID:blank{} ]
FROM
    ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

    RDFXML-SUBJECT[
      var ORIGIN, 
      var NODE as /.*/:/.*/{{
        attributes{{ rdf:blankID{ var NODEID } }}
      }}
    ]
END

% blank node without explicit identifier
CONSTRUCT
  RDFXML-NODE[ var ORIGIN, var NODE, var NIDENT:blank{} ]
FROM
    ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

    RDFXML-SUBJECT[
      var ORIGIN,
      identity var NIDENT var NODE as /.*/:/.*/{{
        attributes{{
          without rdf:about{{}},
          without rdf:nodeID{{}},
          without rdf:ID{{}}
        }}
      }}
    ]
END

CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    var OBJECT
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[  
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as /.*/:/.*/{{
        var P_NS:var P_LN{
          without attributes{{ rdf:parseType{{}} }},
          identity var OIDENT var ONODE as /.*/:/.*/{{}}
        }
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ],
    RDFXML-NODE[ var ORIGIN, identity var OIDENT var ONODE, var OBJECT ]
  ]
END

CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    literal{
      attributes{{
        optional "http://www.w3.org/XML/1998/namespacelang":uri{  var LANG },
        optional "http://www.w3.org/1999/02/22-rdf-syntax-ns#datatype":uri{ var TYPE }
      }},
      var O_TEXT,
    }
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  ns-prefix xml = "http://www.w3.org/XML/1998/namespace"

  and[  
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as /.*/:/.*/{{
        var P_NS:var P_LN{
          var O_TEXT as /.*/,
          attributes{{
            optional xml:lang{ var LANG },
            optional rdf:datatype{ var TYPE }
          }}
        }
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
  ]
END

CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    var O_URI:uri{}
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[  
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as /.*/:/.*/{{
        var P_NS:var P_LN{
          attributes{{ rdf:resource{ O_URI } }}
        }
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
  ]
END

CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    literal{
     optional attributes{{
       "http://www.w3.org/XML/1998/namespacelang":uri{ var LANG }
     }},
     var O_TEXT
    }
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  ns-prefix xml = "http://www.w3.org/XML/1998/namespace"

  and[    
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as /.*/:/.*/{{
        attributes{{
          var P_NS:P_LN{ var O_TEXT },
          optional xml:lang{ var LANG }
        }} where {
          var P_NS != "http://www.w3.org/1999/02/22-rdf-syntax-ns#" and
          var P_NS != "http://www.w3.org/XML/1998/namespace"
        }
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
END

CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    literal{
      attributes{ "http://www.w3.org/1999/02/22-rdf-syntax-ns#datatype":uri{ 
        "http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral"
      }},
      var O_XML
    } 
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[  
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as /.*/:/.*/{{
        var P_NS:P_LN{{
          attributes{{ rdf:parseType{ "Literal" } }},
          var O_XML as /.*/:/.*/{{}}
        }}
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
END

% triple extraction
CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    var O_IDENT:blank{}
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as  /.*/:/.*/{{
        identity var O_IDENT var P_NS:P_LN{{
          attributes{{ rdf:parseType{ "Resource" } }},
        }}
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
  ]
END

%% recursion
CONSTRUCT
  RDFXML-SUBJECT[ var ORIGN, var BLANK ]
FROM
  and[
    rdf:RDF{{ desc identity var IDENT var BLANK as /.*/:/.*/{{}} }},
    RDFXML-SUBJECT[
      var ORIGIN,
      /.*/:/.*/{{
        var BLANK as /.*/:/.*/{{
          attributes{{ rdf:parseType{ "Resource" } }},
        }}
      }}
    ]
  ]
END

%% subject with object as empty property element
CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    &join( var P_NS, var P_LN):uri{},
    var O_IDENT:blank{} 
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[  
    RDFXML-SUBJECT[
       var ORIGIN,
      identity var SIDENT var SNODE as  /.*/:/.*/{{
        identity var O_IDENT var P_NS:P_LN{
          attributes{{
            without rdf:resource{{}},
            without rdf:parseType{{}},
            var A_NS:/.*/{{}} % any other attribute
          }}
        } where {
          var P_NS != "http://www.w3.org/1999/02/22-rdf-syntax-ns#" and
          var P_NS != "http://www.w3.org/XML/1998/namespace"
        }
      }}
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
  ]
END

%% empty property element as subject to it's attributes
CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var S_IDENT:blank{},
    &join( var P_NS, var P_LN):uri{},
    link{ var O_TEXT } 
  ]
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  
  RDFXML-SUBJECT[
    var ORIGIN,
    /.*/:/.*/{{
      identity var S_IDENT /.*/:/.*/{
        attributes{{
          without rdf:resource{{}},
          without rdf:parseType{{}},
          var P_NS:var P_LN{ var O_TEXT } % any other attribute
        }} where {
          var P_NS != "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
        }
      }
    }}
  ]
END

%% case 1, identified subject
CONSTRUCT
  RDF-TRIPLE[
    attributes{ origin{var ORIGIN} },
    var SUBJECT,
    "http://www.w3.org/1999/02/22-rdf-syntax-ns#type":uri{},
    &join( var S_CLASS_NS, var S_CLASS_LN ):uri{}
FROM
  ns-prefix rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"

  and[
    RDFXML-SUBJECT[
      var ORIGIN,
      identity var SIDENT var SNODE as var S_CLASS_NS:var S_CLASS_LN {{
        without attributes{{ rdf:parseType{ "Resource" } }}
      }} where { 
        var S_CLASS_NS != "http://www.w3.org/1999/02/22-rdf-syntax-ns#" and
        var S_CLASS_LN != "Description"
      }
    ],
    RDFXML-NODE[ var ORIGIN, identity var SIDENT var SNODE, var SUBJECT ]
  ]
END