1/* Part of sparkle 2 Copyright 2014-2015 Samer Abdallah (UCL) 3 4 This program is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public License 6 as published by the Free Software Foundation; either version 2 7 of the License, or (at your option) any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public 15 License along with this library; if not, write to the Free Software 16 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 17*/ 18 19:- module(sparkle,[ 20 sparql_endpoint/2 21 , sparql_endpoint/3 22 , current_sparql_endpoint/5 23 , query_goal/3 % Endpoint, Context, Opts 24 , query_phrase/3 % Endpoint, QueryPhrase, Result 25 , query_sparql/3 % Endpoint,QueryText,Result 26 , (??)/1 27 , (??)/2 28 , op(1150,fx,??) 29 , op(1150,xfy,??) 30 ]).
50:- use_module(library(sandbox)). 51:- use_module(library(settings)). 52:- use_module(library(semweb/sparql_client)). 53:- use_module(library(dcg_core)). 54:- use_module(library(dcg_codes)). 55:- use_module(sparql_dcg). 56:- use_module(concurrency). 57 58 59:- dynamic sparql_endpoint/5. 60:- multifile sparql_endpoint/5. 61:- set_prolog_flag(double_quotes, codes). 62 63:- setting(limit,integer,100,'Default SPARQL SELECT limit'). 64:- setting(select_options,list,[distinct(true)],'Default select options'). 65 66:- meta_predicate query_phrase(,,). 67 68sandbox:safe_meta(sparql_dcg:phrase_to_sparql(Phr,_),[Phr]). 69sandbox:safe_primitive(sparql_dcg:select(_,_,_,_,_)). 70sandbox:safe_primitive(sparql_dcg:describe(_,_,_,_)). 71sandbox:safe_primitive(sparql_dcg:describe(_,_,_)). 72sandbox:safe_primitive(sparql_dcg:ask(_,_,_)).
78??(Spec) :- ??(_,Spec).query_goal(EP,Goal,Opts) where Opts is the value of
the setting sparkle:select_options. See query_goal/3 for details.
IF EP is unbound on entry, it is bound to the endpoint from which
the current bindings were obtained.85??(EP,Spec) :- 86 spec_goal_opts(Spec,Goal,Opts), 87 setting(select_options,Opts0), 88 merge_options(Opts,Opts0,Opts1), 89 query_goal(EP,Goal,Opts1). 90 91spec_goal_opts(Opts ?? Goal, Goal, Opts) :- !. 92spec_goal_opts(Goal,Goal,[]). 93 94/* 95 * Assert/declare a new sparql end point 96 */
103sparql_endpoint(EP,Url) :- sparql_endpoint(EP,Url,[]). 104sparql_endpoint(EP,Url,Options) :- 105 url_endpoint(Url,Host,Port,Path), 106 ( sparql_endpoint(EP,Host,Port,Path,_) 107 -> format('% WARNING: Updating already registered SPARQL end point ~w.\n',[Url]), 108 retractall(sparql_endpoint(EP,Host,Port,Path,_)) 109 ), 110 debug(sparkle,'Asserting SPARQL end point ~w: ~w ~w ~w ~w.',[EP,Host,Port,Path,Options]), 111 assert(sparql_endpoint(EP,Host,Port,Path,Options)). 112 113userterm_expansion(:-(sparql_endpoint(EP,Url)), Expanded) :- 114 endpoint_declaration(EP,Url,[],Expanded). 115userterm_expansion(:-(sparql_endpoint(EP,Url,Options)), Expanded) :- 116 endpoint_declaration(EP,Url,Options,Expanded). 117 118endpoint_declaration(EP,Url,Options, sparkle:sparql_endpoint(EP,Host,Port,Path,Options)) :- 119 debug(sparkle,'Declaring SPARQL end point ~w: ~w ~w ~w ~w.',[EP,Host,Port,Path,Options]), 120 url_endpoint(Url,Host,Port,Path). 121 122url_endpoint(Url,Host,Port,Path) :- 123 parse_url(Url,Parsed), 124 member(host(Host),Parsed), 125 member(path(Path),Parsed), 126 (member(port(Port),Parsed);Port=80).
132current_sparql_endpoint(EP,Host,Port,Path,Options) :- 133 sparql_endpoint(EP,Host,Port,Path,Options). 134 135 136% ---------------------------------------------------- 137% Goal-based queries 138% These get translated into phrase-based queries.
sparql_dcg.pl.
If EP is ground on entry, the query is run against the specified endpoint. If EP is unbound on entry, the query is run agains all endpoints in parallel, possibly returning multiple results from each.
(The following applies only to queries that return bindings, not to simple boolean questions, which return only true or false.) Options are as follows:
166query_goal(EP,Goal,Opts) :- 167 findall(EP,sparql_endpoint(EP,_,_,_,_),EPs), 168 term_variables(Goal,Vars), 169 ( Vars = [] % if no variables, do an ASK query, otherwise, SELECT 170 -> phrase_to_sparql(ask(Goal),SPARQL), 171 parallel_query(simple_query(SPARQL),EPs,EP-true) 172 ; Result =.. [row|Vars], 173 setting(limit,DefaultLimit), 174 call_dcg(( option_default_select(limit(Limit),DefaultLimit), 175 option_default_select(autopage(Auto),true), 176 ( {Auto=true} 177 -> {Query = autopage_query(Limit,SPARQL)}, 178 option_default_select(offset(_),_) 179 ; {Query = simple_query(SPARQL)}, 180 cons(limit(Limit)) 181 ) 182 ), Opts, Opts1), 183 phrase_to_sparql(select(Vars,Goal,Opts1),SPARQL), 184 parallel_query(Query,EPs,EP-Result) 185 ). 186 187cons(X,T,[X|T]). 188option_default_select(Opt,Def,O1,O2) :- select_option(Opt,O1,O2,Def). 189simple_query(SPARQL,EP,EP-Result) :- query_sparql(EP,SPARQL,Result). 190autopage_query(Limit,SPARQL,EP,EP-Result) :- autopage(EP,SPARQL,Limit,0,Result). 191 192autopage(EP,SPARQL,Limit,Offset,Result) :- 193 format(string(Q),'~s LIMIT ~d OFFSET ~d',[SPARQL,Limit,Offset]), 194 findall(R,query_sparql(EP,Q,R),Results), 195 ( member(Result,Results) 196 ; length(Results,Limit), % no next page if length(Results) < Limit 197 Offset1 is Offset + Limit, % next batch of results 198 autopage(EP,SPARQL,Limit,Offset1,Result) 199 ). 200 201parallel_query(_,[],_) :- !, fail. 202parallel_query(P,[X],Y) :- !, call(P,X,Y). 203parallel_query(P,Xs,Y) :- 204 maplist(par_goal(P,Y),Xs,Goals), 205 concurrent_or(Y,Goals,[on_error(continue)]). 206 207par_goal(P,Y,X,call(P,X,Y)).
sparql_dcg.pl.
The return type depends on the query:
select(V:list(var), sparql_goal, options) :: sparql_phrase(row(N)) :- length(V,N). describe(resource,sparql_goal) :: sparql_phrase(rdf). describe(resource) :: sparql_phrase(rdf). ask(sparql_goal) :: sparql_phrase(bool). rdf ---> rdf(resource,resource,object). bool ---> true; false.
row(N) is the type of terms of functor row/N.
227query_phrase(EP,Phrase,Result) :- 228 phrase_to_sparql(Phrase,SPARQL), 229 query_sparql(EP,SPARQL,Result). 230 231 232phrase_to_sparql(Phrase,SPARQL) :- 233 term_variables(Phrase,Vars), 234 copy_term(t(Vars,Phrase),t(Vars1,Phrase1)), 235 numbervars(Vars1,0,_), 236 ( phrase(Phrase1,Codes) -> true 237 ; throw(unrecognised_query(Phrase)) 238 ), 239 string_codes(SPARQL,Codes), 240 debug(sparkle,'SPARQL query: ~s',[SPARQL]). 241 242% ---------------------------------------------------- 243% In the end, everything comes through this.
250query_sparql(EP,SPARQL,Result) :-
251 sparql_endpoint(EP,Host,Port,Path,EPOpts),
252 debug(sparkle,'Querying endpoint http://~w:~w~w',[Host,Port,Path]),
253 sparql_query(SPARQL,Result,[host(Host),port(Port),path(Path)|EPOpts])
Query to SPARQL endpoints with a more Prolog-like syntax
Samer Abdallah, Dept. of Computer Science, UCL (2014) Based on Yves Raimond's swic package, but completely re-written.
This module provides a little language for expressing SPARQL queries and a database of known SPARQL endpoints. Queries can be executed across multiple endpoints in parallel. When using auto-paging, multiple queries are made automatically to fetch new bindings as they are needed. For example,
will retrieve all triples from all endpoints in parallel, fetching 100 bindings at a time from each endpoint (assuming the setting sparkle:limit takes it's default value of 100). */