Chris@0: /*  $Id$
Chris@0: 
Chris@0:     Part of SWI-Prolog
Chris@0: 
Chris@0:     Author:        Jan Wielemaker
Chris@0:     E-mail:        wielemak@science.uva.nl
Chris@0:     WWW:           http://www.swi-prolog.org
Chris@0:     Copyright (C): 2004-2006, University of Amsterdam
Chris@0: 
Chris@0:     This program is free software; you can redistribute it and/or
Chris@0:     modify it under the terms of the GNU General Public License
Chris@0:     as published by the Free Software Foundation; either version 2
Chris@0:     of the License, or (at your option) any later version.
Chris@0: 
Chris@0:     This program is distributed in the hope that it will be useful,
Chris@0:     but WITHOUT ANY WARRANTY; without even the implied warranty of
Chris@0:     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
Chris@0:     GNU General Public License for more details.
Chris@0: 
Chris@0:     You should have received a copy of the GNU Lesser General Public
Chris@0:     License along with this library; if not, write to the Free Software
Chris@0:     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
Chris@0: 
Chris@0:     As a special exception, if you link this library with other files,
Chris@0:     compiled with a Free Software compiler, to produce an executable, this
Chris@0:     library does not by itself cause the resulting executable to be covered
Chris@0:     by the GNU General Public License. This exception does not however
Chris@0:     invalidate any other reasons why the executable file might be covered by
Chris@0:     the GNU General Public License.
Chris@0: */
Chris@0: 
Chris@0: :- module(rdfql_util,
Chris@0: 	  [ select_results/6,		% +Distinct, +Offset, +Limit,
Chris@0: 					% 	:SortBy, -Result, :Goal
Chris@0: 	    entailment_module/2		% +Entailment, -Module
Chris@0: 	  ]).
Chris@0: :- use_module(library(nb_set)).
Chris@0: 
Chris@0: :- module_transparent
Chris@0: 	select_results/6,
Chris@0: 	select_results/5.
Chris@0: 
Chris@0: %%	select_results(+Distinct, +Offset, +Limit, :SortBy, -Result, :Goal)
Chris@0: %	
Chris@0: %	Select results for the  template   Result  on  backtracking over
Chris@0: %	Goal.
Chris@0: %	
Chris@0: %	@param Distinct
Chris@0: %	Iff 'distinct', only consider distinct solutions
Chris@0: %		
Chris@0: %	@param Offset
Chris@0: %	Skip the first Offset results.  Offset is applied after
Chris@0: %	Distinct and SortBy
Chris@0: %		
Chris@0: %	@param Limit
Chris@0: %	Only return the first Limit results. Limit is applied
Chris@0: %	after Distinct, SortBy and Offset. The value 'inf'
Chris@0: %	returns all values.
Chris@0: %		
Chris@0: %	@param SortBy
Chris@0: %	Either 'unsorted' or the name of a predicate that sorts
Chris@0: %	the result-set by calling call(SortBy, UnSorted, Sorted)
Chris@0: 
Chris@0: select_results(Distinct, Offset, Limit, unsorted, Result, Goal) :- !,
Chris@0: 	select_results(Distinct, Offset, Limit, Result, Goal).
Chris@0: select_results(Distinct, Offset, Limit, order_by(Cols), Result, Goal) :- !,
Chris@0: 	term_variables(Cols, Vars),
Chris@0: 	SortKey =.. [v|Vars],
Chris@0: 	findall(SortKey-Result, Goal, Results0),
Chris@0: 	(   Distinct == distinct
Chris@0: 	->  sort(Results0, Results1)
Chris@0: 	;   keysort(Results0, Results1)
Chris@0: 	),
Chris@0: 	apply_offset(Offset, Results1, Results2),
Chris@0: 	apply_limit(Limit, Results2, Results),
Chris@0: 	member(_Key-Result, Results).
Chris@0: 	
Chris@0: %%	select_results(+Distinct, +Offset, +Limit, -Result, :Goal)
Chris@0: %	
Chris@0: %	Unsorted version. In this case we can avoid first collecting all
Chris@0: %	results.
Chris@0: 
Chris@0: select_results(distinct, Offset, Limit, Result, Goal) :- !,
Chris@0: 	term_variables(Result, Vars),
Chris@0: 	V =.. [v|Vars],
Chris@0: 	empty_nb_set(Set),
Chris@0: 	Counter = count(0),
Chris@0: 	Goal,
Chris@0: 	   add_nb_set(V, Set, New),
Chris@0: 	   New == true,
Chris@0: 	   apply_limit(Counter, Offset, Limit, Last),
Chris@0: 	   ( Last == true -> ! ; true ).
Chris@0: select_results(_, 0, inf, _, G) :- !,
Chris@0: 	G.
Chris@0: select_results(_, Offset, Limit, _, G) :- !,
Chris@0: 	Counter = count(0),
Chris@0: 	G,
Chris@0: 	    apply_limit(Counter, Offset, Limit, Last),
Chris@0: 	    ( Last == true -> ! ; true ).
Chris@0: 
Chris@0: apply_limit(_, 0, inf, false) :- !.
Chris@0: apply_limit(Counter, Offset, Limit, Last) :-
Chris@0: 	arg(1, Counter, N0),
Chris@0: 	N is N0 + 1,
Chris@0: 	nb_setarg(1, Counter, N),
Chris@0: 	N > Offset,
Chris@0: 	(   Limit \== inf,
Chris@0: 	    N =:= Offset+Limit
Chris@0: 	->  Last = true
Chris@0: 	;   Last = false
Chris@0: 	).
Chris@0: 
Chris@0: apply_offset(0, List, List) :- !.
Chris@0: apply_offset(N, [_|T], List) :-
Chris@0: 	N > 0,
Chris@0: 	N2 is N - 1,
Chris@0: 	apply_offset(N2, T, List).
Chris@0: 
Chris@0: apply_limit(inf, List, List) :- !.
Chris@0: apply_limit(0, _, []).
Chris@0: apply_limit(N, [H|T0], [H|T]) :-
Chris@0: 	N > 0,
Chris@0: 	N2 is N - 1,
Chris@0: 	apply_offset(N2, T0, T).
Chris@0: 
Chris@0: 
Chris@0: 		 /*******************************
Chris@0: 		 *	     ENTAILMENT		*
Chris@0: 		 *******************************/
Chris@0: 
Chris@0: %%	entailment_module(+Entailment, -Module)
Chris@0: %	
Chris@0: %	Find the Prolog module implementing the   entailment rules for a
Chris@0: %	semantic web language.
Chris@0: 
Chris@0: entailment_module(Entailment, Module) :-
Chris@0: 	serql:entailment(Entailment, Module), !.
Chris@0: entailment_module(Entailment, _) :-
Chris@0: 	throw(error(existence_error(entailment, Entailment), _)).
Chris@0: 
Chris@0: :- multifile
Chris@0: 	serql:entailment/2.
Chris@0: