/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@vu.nl WWW: http://www.swi-prolog.org Copyright (C): 2005-2012, University of Amsterdam VU University Amsterdam This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA As a special exception, if you link this library with other files, compiled with a Free Software compiler, to produce an executable, this library does not by itself cause the resulting executable to be covered by the GNU General Public License. This exception does not however invalidate any other reasons why the executable file might be covered by the GNU General Public License. */ :- module(sparql, [ sparql_query/3, % +Query, -Result, +Options sparql_compile/3, % +Query, -Compiled, +Options sparql_run/2 % +Compiled, -Reply ]). :- use_module(library(option)). :- use_module(library(assoc)). :- use_module(library(apply)). :- use_module(library(semweb/rdf_db), [rdf_is_bnode/1]). :- use_module(library(semweb/rdf_optimise)). :- use_module(library(settings)). :- use_module(sparql_grammar). :- use_module(sparql_runtime). :- use_module(rdfql_util). :- use_module(library(settings)). :- include(entailment(load)). :- multifile function/2. % user-defined functions :- setting(entailment, atom, rdf, 'Default entailment used for SPARQL queries'). %% sparql_query(+Query, -Reply, +Options) % % Where Query is either a SPARQL query text or a parsed % query. Reply depends on the type of query: % % |SELECT | row(Col1, Col2, ....) | % |CONSTRUCT | rdf(S,P,O) | % |DESCRIBE | rdf(S,P,O) | % |ASK | Reply == true or failure of pred | % % Options are: % % * entailment(Entailment) % Specify the entailment module used. The default is % controlled by the setting =|sparql:entailment|=. % % * base_uri(Base) % Specify the base IRI to use for parsing the query % % * type(-Type) % Returns one of select(-VarNames), construct, describe or % ask. % % * ordered(-Bool) % True if query contains an ORDER BY clause % % * distinct(-Bool) % True if query contains a DISTINCT clause sparql_query(Query, Reply, Options) :- sparql_compile(Query, Compiled, Options), sparql_run(Compiled, Reply). %% sparql_compile(+Query, -Compiled, +Options) % % Performs the compilation pass of solving a SPARQL query. % Splitting serves two purposes. The result of the compilation can % be cached if desired and through Options we can get information % about the parsed query. sparql_compile(Query, sparql_query(Optimised, ReplyTemplate, Module), Options) :- sparql_parse(Query, Parsed, Options), optimise(Parsed, Optimised, Options), ( option(entailment(Entailment), Options) -> true ; setting(entailment, Entailment) ), option(type(Type), Options, _), option(ordered(Order), Options, _), option(distinct(Distinct), Options, _), entailment_module(Entailment, Module), prepare(Parsed, Type, Order, Distinct, ReplyTemplate). prepare(select(Vars, _, _, S), select(Names), O, D, Reply) :- !, select_result(Vars, Reply, Names), solutions(S, O, D). prepare(construct(_,_,_,S), construct, O, D, _) :- !, solutions(S, O, D). prepare(ask(_,_,S), ask, O, D, _) :- !, solutions(S, O, D). prepare(describe(_,_,_,S), describe, O, D, _) :- !, solutions(S, O, D). prepare(update(_), update, false, false, _) :- !. prepare(Query, Type, _, _, _) :- nonvar(Type), functor(Type, Expected, _), functor(Query, Found, _), throw(error(type_error(query_type(Expected), Found), _)). solutions(distinct(S), O, true) :- !, solutions(S, O). solutions(S, O, false) :- solutions(S, O). solutions(solutions(_Group, _Having, _Aggregate, unsorted, _, _), O) :- !, O = false. solutions(_, true). %% optimise(+Parsed, -Optimised, +Options) is det. % % Perform sparql query optimization using rdf_optimise/2. % Currently, UPDATE requests are not optimized. % % @tbd The UPDATE modify requests involve a query and must be % optimized. optimise(update(Updates), update(Updates), _) :- !. optimise(Parsed, Optimised, Options) :- ( option(optimise(Optimise), Options) -> Optimise == true ; setting(cliopatria:optimise_query, true) ), prolog_goal(Parsed, Goal0), simplify_group(Goal0, Goal1), optimise_eval(Goal1, Goal2), rdf_optimise(Goal2, Goal3), !, bind_null(Goal3, Goal, Options), set_prolog_goal(Parsed, Goal, Optimised). optimise(Parsed, Optimised, Options) :- prolog_goal(Parsed, Goal0), simplify_group(Goal0, Goal1), bind_null(Goal1, Goal, Options), set_prolog_goal(Parsed, Goal, Optimised). % remove the outer SPARQL group. It has no meaning and reduces % readability. simplify_group(sparql_group(G), G) :- !. simplify_group(sparql_group(G, VIn, VOut), G) :- VIn = VOut, !. simplify_group(Goal, Goal). bind_null(Goal0, Goal, Options) :- option(bind_null(true), Options), !, serql_select_bind_null(Goal0, Goal). bind_null(Goal, Goal, _). prolog_goal(select(_Proj, _DataSets, Goal, _Solutions), Goal). prolog_goal(construct(_Templ, _DataSets, Goal, _Solutions), Goal). prolog_goal(ask(_DataSets, Goal, _Solutions), Goal). prolog_goal(describe(_Proj, _DataSets, Goal, _Solutions), Goal). prolog_goal(sparql_group(Goal), Goal). prolog_goal(sparql_group(Goal,_VA,_VZ), Goal). set_prolog_goal(select(Proj, DataSets, _Goal, Solutions), Goal, select(Proj, DataSets, Goal, Solutions)). set_prolog_goal(construct(Templ, DataSets, _Goal, Solutions), Goal, construct(Templ, DataSets, Goal, Solutions)). set_prolog_goal(ask(DataSets, _Goal, Solutions), Goal, ask(DataSets, Goal, Solutions)). set_prolog_goal(describe(Proj, DataSets, _Goal, Solutions), Goal, describe(Proj, DataSets, Goal, Solutions)). set_prolog_goal(sparql_group(_Goal), Goal, Goal). set_prolog_goal(sparql_group(_Goal,VA,VZ), Goal, (Goal,VA=VZ)). %% optimise_eval(+Goal0, -Goal) is det. % % Perform partial evaluation on sparql_true/1 and sparql_eval/2 % goals. optimise_eval(GoalIn, GoalOut) :- annotate_variables(GoalIn, Vars), optimise_annotated(GoalIn, GoalOut), unbind_variables(Vars). %% annotate_variables(+Goal, -Vars) is det. % % Annotate variables that appear in Goal. The annotation is a % variable attribute named =annotations= and the value of this % attribute is a list of annotations. annotate_variables(Goal, Vars) :- empty_assoc(Vars0), annotate_vars(Goal, Vars0, Vars). annotate_vars(Var, _, _) :- var(Var), !, instantiation_error(Var). annotate_vars((A,B), Vars0, Vars) :- !, annotate_vars(A, Vars0, Vars1), annotate_vars(B, Vars1, Vars). annotate_vars((A;B), Vars0, Vars) :- !, annotate_vars(A, Vars0, Vars1), annotate_vars(B, Vars1, Vars). annotate_vars((A*->B), Vars0, Vars) :- !, annotate_vars(A, Vars0, Vars1), annotate_vars(B, Vars1, Vars). annotate_vars(sparql_group(G), Vars0, Vars) :- !, annotate_vars(G, Vars0, Vars). annotate_vars(sparql_group(G, _, _), Vars0, Vars) :- !, annotate_vars(G, Vars0, Vars). annotate_vars(rdf(S,P,_), Vars0, Vars) :- !, annotate_var(S, resource, Vars0, Vars1), annotate_var(P, resource, Vars1, Vars). annotate_vars(rdf(S,P,_,G), Vars0, Vars) :- !, annotate_var(S, resource, Vars0, Vars1), annotate_var(P, resource, Vars1, Vars2), annotate_var(G, resource, Vars2, Vars). annotate_vars(_, Vars, Vars). annotate_var(V, Type, Vars0, Vars) :- var(V), ( get_attr(V, annotations, A0) -> \+ memberchk(Type, A0) ; A0 = [] ), !, put_attr(V, annotations, [Type|A0]), put_assoc(V, Vars0, true, Vars). annotate_var(_, _, Vars, Vars). unbind_variables(VarAssoc) :- assoc_to_keys(VarAssoc, VarList), maplist(unbind_var, VarList). unbind_var(V) :- del_attr(V, annotations). %% optimise_eval(+GoalIn, -GoalOut) optimise_annotated((A0,B0), (A,B)) :- !, optimise_annotated(A0, A), optimise_annotated(B0, B). optimise_annotated((A0;B0), (A;B)) :- !, optimise_annotated(A0, A), optimise_annotated(B0, B). optimise_annotated((A0*->B0), (A*->B)) :- !, optimise_annotated(A0, A), optimise_annotated(B0, B). optimise_annotated(sparql_group(G0), sparql_group(G)) :- !, optimise_annotated(G0, G). optimise_annotated(sparql_group(G0, OV, IV), sparql_group(G, OV, IV)) :- !, optimise_annotated(G0, G). optimise_annotated(sparql_true(E), G) :- !, sparql_simplify(sparql_true(E), G). optimise_annotated(sparql_eval(E,V), G) :- !, sparql_simplify(sparql_eval(E,V), G). optimise_annotated(G, G). %% sparql_run(+Compiled, -Reply) is nondet. % % Runs a compiled SPARQL query, returning the result incrementally % on backtracking. Provided there are no errors in the SPARQL % implementation the only errors this can produce are % resource-related errors. sparql_run(sparql_query(Parsed, Reply, Module), Reply) :- sparql_reset_bnodes, sparql_run(Parsed, Reply, Module). sparql_run(select(_Vars, _DataSets, Query, Solutions), Reply, Module) :- select_results(Solutions, Reply, Module:Query). sparql_run(construct(Triples, _DataSets, Query, Solutions), Reply, Module) :- select_results(Solutions, Reply, Module:( Query, rdfql_triple_in(Reply, Triples) )). sparql_run(ask(_DataSets, Query, _Solutions), Result, Module) :- ( Module:Query -> Result = true ; Result = false ). sparql_run(describe(IRIs, _DataSets, Query, Solutions), Reply, Module) :- select_results(Solutions, Reply, ( Module:Query, member(IRI, IRIs) )), sparql_describe(IRI, Module, Reply). sparql_run(update(Updates), Result, Module) :- ( Module:sparql_update(Updates) -> Result = true ; Result = false ). %% select_results(+Spec, -Reply, :Goal) % % Apply ordering and limits on result-set. % % @tbd Handle =reduced= :- meta_predicate select_results(+,+,0). :- public select_results/3. % used on sparql_subquery/4 select_results(distinct(solutions(Group, Having, Agg, Order, Limit, Offset)), Reply, Goal) :- !, select_results(distinct, Group, Having, Agg, Offset, Limit, Order, Reply, Goal). select_results(reduced(Solutions), Reply, Goal) :- !, select_results(Solutions, Reply, Goal). select_results(solutions(Group, Having, Agg, Order, Limit, Offset), Reply, Goal) :- select_results(all, Group, Having, Agg, Offset, Limit, Order, Reply, Goal). %% select_result(+Bindings, -Row, -Names) is det. % % Transform the list Bindings of the form Name=Var into a Row term % of the form row(Col1, Col2, ...) and a term names(Name1, ...). % For example: % % == % ?- select_result([x=1,y=2], Row, Names). % Row = row(1,2), Names = names(x,y) % == select_result(Bindings, Row, Names) :- vars_in_bindings(Bindings, Vars, VarNames), Names =.. [names|VarNames], Row =.. [row|Vars]. vars_in_bindings([], [], []). vars_in_bindings([Name=Var|T0], [Var|T], [Name|NT]) :- vars_in_bindings(T0, T, NT). %% sparql_describe(+IRI, -Triple) % % Return -on backtracking- triples that describe IRI. The % documentation does not specify which triples must be returned % for a description. As a way to get started we simply return all % direct properties. sparql_describe(_Var=IRI, Module, Triple) :- !, sparql_describe(IRI, Module, Triple). sparql_describe(IRI, Module, Triple) :- empty_assoc(Seen), sparql_describe(IRI, Module, Triple, Seen). sparql_describe(IRI, Module, Triple, Seen) :- Module:rdf(IRI, P, O), ( rdf_is_bnode(O), \+ get_assoc(O, Seen, true) -> ( Triple = rdf(IRI, P, O) ; put_assoc(O, Seen, true, Seen2), sparql_describe(O, Module, Triple, Seen2) ) ; Triple = rdf(IRI, P, O) ).