1/*  Part of ClioPatria SeRQL and SPARQL server
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2018, University of Amsterdam
    7    All rights reserved.
    8
    9    Redistribution and use in source and binary forms, with or without
   10    modification, are permitted provided that the following conditions
   11    are met:
   12
   13    1. Redistributions of source code must retain the above copyright
   14       notice, this list of conditions and the following disclaimer.
   15
   16    2. Redistributions in binary form must reproduce the above copyright
   17       notice, this list of conditions and the following disclaimer in
   18       the documentation and/or other materials provided with the
   19       distribution.
   20
   21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   32    POSSIBILITY OF SUCH DAMAGE.
   33*/
   34
   35:- module(sparql_json_result,
   36          [ sparql_write_json_result/3  % +Out, +Result, +Options
   37          ]).   38:- use_module(library(http/http_json)).   39:- use_module(library(sgml_write)).   40:- use_module(library(apply)).   41:- use_module(library(option)).   42:- use_module(library(semweb/rdf_db)).

   51sparql_json_mime_type(application/'sparql-results+json; charset=UTF-8').

 sparql_write_json_result(+Out:stream, +Result, +Options) is det

Emit results from a SPARQL query as JSON.

See also

- http://www.w3.org/TR/rdf-sparql-json-res/

   59sparql_write_json_result(Out, select(VarTerm, Rows), Options) :-
   60    VarTerm =.. [_|VarNames],
   61    JSON = json([ head    = json([vars=VarNames]),
   62                  results = json([bindings=Bindings])
   63                ]),
   64    maplist(row_to_json(VarNames), Rows, Bindings),
   65    (   option(content_type(_), Options)
   66    ->  JSONOptions = Options
   67    ;   sparql_json_mime_type(Mime),
   68        JSONOptions = [content_type(Mime)|Options]
   69    ),
   70    with_output_to(Out, reply_json(JSON, JSONOptions)).
   71sparql_write_json_result(Out, ask(True), Options) :-
   72    JSON = json([ head    = json([]),
   73                  boolean = @(True)
   74                ]),
   75    (   option(content_type(_), Options)
   76    ->  JSONOptions = Options
   77    ;   sparql_json_mime_type(Mime),
   78        JSONOptions = [content_type(Mime)|Options]
   79    ),
   80    with_output_to(Out, reply_json(JSON, JSONOptions)).
   81
   82
   83row_to_json(Vars, Row, json(Bindings)) :-
   84    var_col_bindings(Vars, 1, Row, Bindings).
   85
   86var_col_bindings([], _, _, []).
   87var_col_bindings([V0|T0], I, Row, Bindings) :-
   88    arg(I, Row, Value),
   89    I2 is I + 1,
   90    (   Value = '$null$'            % also catches variables
   91    ->  var_col_bindings(T0, I2, Row, Bindings)
   92    ;   Bindings = [V0=json(JSON)|T],
   93        rdf_term_to_json(Value, JSON),
   94        var_col_bindings(T0, I2, Row, T)
   95    ).

 rdf_term_to_json(+RDFTerm, -JsonTerm)

convert an rdf term to a json term.

To be done

- : Handle blank nodes.

  104rdf_term_to_json(literal(Lit), Object) :-
  105    !,
  106    Object = [type=literal, value=Txt|Rest],
  107    literal_to_json(Lit, Txt, Rest).
  108rdf_term_to_json(URI0, Object) :-
  109    rdf_global_id(URI0, URI),
  110    Object = [type=Type, value=URI],
  111    object_uri_type(URI, Type).

 literal_to_json(+Literal, -Text, -Attributes)

Extract text and Attributes from Literal resource.

  117literal_to_json(lang(Lang, Text), Text, ['xml:lang'=Lang]) :- !.
  118literal_to_json(type(Type, Text0), Text, [datatype=Type]) :-
  119    !,
  120    to_text(Type, Text0, Text).
  121literal_to_json(Txt, Txt, []).
  122
  123to_text(_Type, Text, Text) :-
  124    atomic(Text).
  125to_text(Type, DOM, Text) :-
  126    rdf_equal(Type, rdf:'XMLLiteral'),
  127    !,
  128    with_output_to(string(Text),
  129                   xml_write(DOM, [header(false)])),
  130    atomic(Text).

 object_uri_type(+URI, -Type)

Type is one of bnode or uri.

  136object_uri_type(URI, Type) :-
  137    (   rdf_is_bnode(URI)
  138    ->  Type = bnode
  139    ;   Type = uri
  140    ).
  141
  142                 /*******************************
  143                 *   INTERACTIVE QUERY RESULT   *
  144                 *******************************/
  145
  146:- multifile
  147    rdf_io:write_table/4.  148
  149rdf_io:write_table(json, _, Rows, Options) :-
  150    memberchk(variables(Vars), Options),
  151    !,
  152    (   is_list(Vars)
  153    ->  VarTerm =.. [vars|Vars]
  154    ;   VarTerm = Vars
  155    ),
  156    sparql_write_json_result(current_output, select(VarTerm, Rows),
  157                             [ content_type(text/plain),
  158                               Options
  159                             ])