1/*  Part of ClioPatria SeRQL and SPARQL server
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@uva.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (C): 2009, University of Amsterdam
    7
    8    This program is free software; you can redistribute it and/or
    9    modify it under the terms of the GNU General Public License
   10    as published by the Free Software Foundation; either version 2
   11    of the License, or (at your option) any later version.
   12
   13    This program is distributed in the hope that it will be useful,
   14    but WITHOUT ANY WARRANTY; without even the implied warranty of
   15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   16    GNU General Public License for more details.
   17
   18    You should have received a copy of the GNU General Public
   19    License along with this library; if not, write to the Free Software
   20    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   21
   22    As a special exception, if you link this library with other files,
   23    compiled with a Free Software compiler, to produce an executable, this
   24    library does not by itself cause the resulting executable to be covered
   25    by the GNU General Public License. This exception does not however
   26    invalidate any other reasons why the executable file might be covered by
   27    the GNU General Public License.
   28*/
   29
   30:- module(sparql_json_result,
   31	  [ sparql_write_json_result/3	% +Out, +Result, +Options
   32	  ]).   33:- use_module(library(http/http_json)).   34:- use_module(library(sgml_write)).   35:- use_module(library(apply)).   36:- use_module(library(option)).   37:- use_module(library(semweb/rdf_db)).   38
   39/** <module> Write SPARQL results as JSON
   40
   41@tbd	Support other SPARQL request results
   42@author Jan Wielemaker
   43@author Michiel Hildebrand
   44*/
   45
   46sparql_json_mime_type(application/'sparql-results+json; charset=UTF-8').
   47
   48%%	sparql_write_json_result(+Out:stream, +Result, +Options) is det.
   49%
   50%	Emit results from a SPARQL query as JSON.
   51%
   52%	@see http://www.w3.org/TR/rdf-sparql-json-res/
   53
   54sparql_write_json_result(Out, select(VarTerm, Rows), Options) :-
   55	VarTerm =.. [_|VarNames],
   56	JSON = json([ head    = json([vars=VarNames]),
   57		      results = json([bindings=Bindings])
   58		    ]),
   59	maplist(row_to_json(VarNames), Rows, Bindings),
   60	(   option(content_type(_), Options)
   61	->  JSONOptions = Options
   62	;   sparql_json_mime_type(Mime),
   63	    JSONOptions = [content_type(Mime)|Options]
   64	),
   65	with_output_to(Out, reply_json(JSON, JSONOptions)).
   66sparql_write_json_result(Out, ask(True), Options) :-
   67	JSON = json([ head    = json([]),
   68		      boolean = @(True)
   69		    ]),
   70	(   option(content_type(_), Options)
   71	->  JSONOptions = Options
   72	;   sparql_json_mime_type(Mime),
   73	    JSONOptions = [content_type(Mime)|Options]
   74	),
   75	with_output_to(Out, reply_json(JSON, JSONOptions)).
   76
   77
   78row_to_json(Vars, Row, json(Bindings)) :-
   79	var_col_bindings(Vars, 1, Row, Bindings).
   80
   81var_col_bindings([], _, _, []).
   82var_col_bindings([V0|T0], I, Row, Bindings) :-
   83	arg(I, Row, Value),
   84	I2 is I + 1,
   85	(   Value = '$null$'		% also catches variables
   86	->  var_col_bindings(T0, I2, Row, Bindings)
   87	;   Bindings = [V0=json(JSON)|T],
   88	    rdf_term_to_json(Value, JSON),
   89	    var_col_bindings(T0, I2, Row, T)
   90	).
   91
   92
   93%%	rdf_term_to_json(+RDFTerm, -JsonTerm)
   94%
   95%	convert an rdf term to a json term.
   96%
   97%	@tbd: Handle blank nodes.
   98
   99rdf_term_to_json(literal(Lit), Object) :- !,
  100	Object = [type=literal, value=Txt|Rest],
  101	literal_to_json(Lit, Txt, Rest).
  102rdf_term_to_json(URI0, Object) :-
  103	rdf_global_id(URI0, URI),
  104	Object = [type=Type, value=URI],
  105	object_uri_type(URI, Type).
  106
  107%%	literal_to_json(+Literal, -Text, -Attributes)
  108%
  109%	Extract text and Attributes from Literal resource.
  110
  111literal_to_json(lang(Lang, Text), Text, ['xml:lang'=Lang]) :- !.
  112literal_to_json(type(Type, Text0), Text, [datatype=Type]) :- !,
  113	to_text(Type, Text0, Text).
  114literal_to_json(Txt, Txt, []).
  115
  116to_text(_Type, Text, Text) :-
  117	atomic(Text).
  118to_text(Type, DOM, Text) :-
  119	rdf_equal(Type, rdf:'XMLLiteral'), !,
  120	with_output_to(string(Text),
  121		       xml_write(DOM, [header(false)])),
  122	atomic(Text).
  123
  124%%	object_uri_type(+URI, -Type)
  125%
  126%	Type is one of bnode or uri.
  127
  128object_uri_type(URI, Type) :-
  129	(   rdf_is_bnode(URI)
  130	->  Type = bnode
  131	;   Type = uri
  132	).
  133
  134		 /*******************************
  135		 *   INTERACTIVE QUERY RESULT	*
  136		 *******************************/
  137
  138:- multifile
  139	rdf_io:write_table/4.  140
  141rdf_io:write_table(json, _, Rows, Options) :-
  142	memberchk(variables(Vars), Options), !,
  143	(   is_list(Vars)
  144	->  VarTerm =.. [vars|Vars]
  145	;   VarTerm = Vars
  146	),
  147	sparql_write_json_result(current_output, select(VarTerm, Rows),
  148				 [ content_type(text/plain),
  149				   Options
  150				 ])