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1 /* $Id$
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2
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3 Part of SWI-Prolog
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4
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5 Author: Jan Wielemaker
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6 E-mail: wielemak@science.uva.nl
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7 WWW: http://www.swi-prolog.org
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8 Copyright (C): 2004-2006, University of Amsterdam
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9
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10 This program is free software; you can redistribute it and/or
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11 modify it under the terms of the GNU General Public License
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12 as published by the Free Software Foundation; either version 2
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13 of the License, or (at your option) any later version.
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14
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15 This program is distributed in the hope that it will be useful,
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16 but WITHOUT ANY WARRANTY; without even the implied warranty of
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17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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18 GNU General Public License for more details.
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19
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20 You should have received a copy of the GNU Lesser General Public
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21 License along with this library; if not, write to the Free Software
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22 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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23
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24 As a special exception, if you link this library with other files,
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25 compiled with a Free Software compiler, to produce an executable, this
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26 library does not by itself cause the resulting executable to be covered
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27 by the GNU General Public License. This exception does not however
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28 invalidate any other reasons why the executable file might be covered by
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29 the GNU General Public License.
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30 */
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31
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32 :- module(sparql_client,
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33 [ sparql_query/3, % +Query, -Row, +Options
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34 sparql_set_server/1 % +Options
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35 ]).
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36 :- use_module(library('http/http_open')).
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37 :- use_module(sparql_xml_result).
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38 :- use_module(library(lists)).
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39 :- use_module(library(rdf)).
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40
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41
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42 %% sparql_query(+Query, -Result, +Options) is nondet.
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43 %
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44 % Execute a SPARQL query on an HTTP SPARQL endpoint. Query is an
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45 % atom that denotes the query. Result is unified to a term
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46 % rdf(S,P,O) for =construct= queries and row(...) for =select=
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47 % queries.
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48
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49 sparql_query(Query, Row, Options) :-
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50 sparql_param(host(Host), Options),
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51 sparql_param(port(Port), Options),
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52 sparql_param(path(Path), Options),
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53 http_open([ protocol(http),
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54 host(Host),
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55 port(Port),
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56 path(Path),
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57 search([ query = Query
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58 ])
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59 ], In,
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60 [ header(content_type, ContentType)
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61 ]),
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62 plain_content_type(ContentType, CleanType),
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63 read_reply(CleanType, In, Row).
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64
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65 read_reply('application/rdf+xml', In, Row) :- !,
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66 call_cleanup(load_rdf(stream(In), RDF), close(In)),
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67 member(Row, RDF).
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68 read_reply('application/sparql-result+xml', In, Row) :- !,
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69 call_cleanup(sparql_read_xml_result(stream(In), Result),
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70 close(In)),
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71 xml_result(Result, Row).
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72 read_reply(Type, In, _) :-
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73 close(In),
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74 throw(error(domain_error(sparql_result_document, Type), _)).
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75
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76 plain_content_type(Type, Plain) :-
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77 sub_atom(Type, B, _, _, (;)), !,
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78 sub_string(Type, 0, B, _, Main),
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79 normalize_space(atom(Plain), Main).
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80 plain_content_type(Type, Type).
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81
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82 xml_result(ask(Bool), Result) :- !,
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83 Result = Bool.
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84 xml_result(select(_VarNames, Rows), Result) :-
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85 member(Result, Rows).
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86
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87
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88
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89
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90
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91 /*******************************
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92 * SETTINGS *
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93 *******************************/
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94
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95 :- dynamic
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96 sparql_setting/1.
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97
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98 sparql_param(Param, Options) :-
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99 memberchk(Param, Options), !.
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100 sparql_param(Param, _Options) :-
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101 sparql_setting(Param), !.
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102 sparql_param(Param, _Options) :-
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103 functor(Param, Name, _),
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104 throw(error(existence_error(option, Name), _)).
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105
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106 %% sparql_set_server(+OptionOrList)
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107 %
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108 % Set sparql server default options. Provided defaults are:
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109 % host, port and repository. For example:
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110 %
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111 %% set_sparql_default([ host(localhost),
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112 %% port(8080)
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113 %% repository(world)
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114 % ])
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115
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116 sparql_set_server([]) :- !.
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117 sparql_set_server([H|T]) :- !,
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118 sparql_set_server(H),
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119 sparql_set_server(T).
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120 sparql_set_server(Term) :-
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121 functor(Term, Name, Arity),
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122 functor(Unbound, Name, Arity),
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123 retractall(sparql_setting(Unbound)),
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124 assert(sparql_setting(Term)).
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