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(sparql_dcg,[ 20 select//3 21 , describe//1 22 , describe//2 23 , ask//1 24 ]).

A simple DCG for generating a subset of SPARQL

sparql_goal ---> (sparql_goal, sparql_goal) % conjunction
               ; (sparql_goal; sparql_goal) % disjunction
               ; rdf(resource,resource,object)
               ; filter(cond)
               .

resource :< object. % any resource is an object

literal(+literal)   :: object.  % any ground literal is an object
atomic              :< literal. % any atomic can be a plain literal
lang(atom,atom)     :: literal. % literal with language
type(resource,atom) :: literal. % typed literal

object   :< expr. % any object is an expr
number   :< expr. % Prolog numerical values can also be expressions

condition ---> (cond , cond)
             ; (cond ; cond)
             ; \+ cond
             ; expr == expr
             ; expr \= expr
             ; expr >= expr
             ; expr =< expr
             ; expr < expr
             ; expr > expr
             ; between(expr,expr,expr)
             ; in(object,list(object))
             ; regex(pattern,value)
             ; bound(object)
             ; blank(resource)
             ; uri(object)
             ; literal(object)
             .

expr ---> expr + expr
        ; expr - expr
        ; expr * expr
        ; expr / expr
        ; +expr
        ; -expr
        ; str(expr)
        ; lang(expr)
        ; datatype(expr)
        .

var ---> '$VAR'(integer)
       ; '@'        % anonymous blank node
       ; '@'(atom)  % nonymous blank node
       .

var :< resource
var :< literal

Samer Abdallah, Dept. of Computer Science, UCL (2014) /

87:- use_module(library(semweb/rdf_db), [rdf_global_object/2, rdf_global_id/2]). 88:- use_module(library(dcg_core)). 89:- use_module(library(dcg_codes)). 90 91:- set_prolog_flag(double_quotes, codes).

98select(Vars,Goal,Options) --> 99 "SELECT ", 100 if_option(distinct(Distinct), if(Distinct=true, " DISTINCT "),Options,O1), 101 seqmap_with_sep(" ",expr,Vars), " ", 102 where(Goal), 103 if_option(order_by(OB), (" ORDER BY ", expr(OB)), O1,O2), 104 if_option(limit(Limit), (" LIMIT ", at(Limit)), O2,O3), 105 if_option(offset(Offs), (" OFFSET ", at(Offs)), O3,O4), 106 {check_remaining_options(O4)}. 107 108check_remaining_options([]) :- !. 109check_remaining_options(Opts) :- throw(unrecognised_options(Opts)). 110 111if_option(Opt,Phrase,O1,O2) --> 112 ( {select_option(Opt,O1,O2)} -> call_dcg(Phrase); {O2=O1}).

132goal(G1;G2) --> brace(goal(G1)), " UNION ", brace(goal(G2)). 133goal(\+G) --> "FILTER NOT EXISTS ", brace(goal(G)). %NB consider MINUS { ... } also 134goal((G1,G2)) --> goal(G1), " . ", goal(G2). 135goal(conj(GS)) --> seqmap_with_sep(" , ",goal,GS). 136 137goal(rdf(S,P,O)) --> 138 { rdf_global_object(O,OO) }, 139 resource(S), " ", 140 resource(P), " ", 141 object(OO). 142 143goal(filter(Cond)) --> "FILTER ", cond(Cond). 144 145:- op(1150,fx,p). 146p(X) --> paren(X). 147 148cond(\+C) --> p "! ", cond(C). 149cond((X,Y)) --> p cond(X), " && ", cond(Y). 150cond((X;Y)) --> p cond(X), " || ", cond(Y). 151cond(X==Y) --> p expr(X), " = ", expr(Y). 152cond(X\=Y) --> p expr(X), " != ", expr(Y). 153cond(X=<Y) --> p expr(X), " <= ", expr(Y). 154cond(X>=Y) --> p expr(X), " >= ", expr(Y). 155cond(X>Y) --> p expr(X), " > ", expr(Y). 156cond(X<Y) --> p expr(X), " < ", expr(Y). 157cond(between(L,U,X)) --> cond((L=<X,X=<U)). 158cond(in(X,Ys)) --> p expr(X), " in ", (p seqmap_with_sep(", ",expr,Ys)). 159cond(regex(P,V)) --> "regex(", object(V), ",", quote(at(P)), ")". 160cond(regex(P,V,F)) --> "regex(", object(V), ",", quote(at(P)), ",", quote(at(F)), ")". 161cond(bound(V)) --> "bound(", object(V), ")". 162cond(uri(V)) --> "isURI(", object(V), ")". 163cond(blank(V)) --> "isBLANK(", object(V), ")". 164cond(literal(V)) --> "isLITERAL(", object(V), ")". 165 166expr(str(V)) --> "STR(", object(V), ")". 167expr(lang(V)) --> "LANG(", object(V), ")". 168expr(count(X)) --> "COUNT(", expr(X), ")". 169expr(datatype(V)) --> "DATATYPE(", object(V), ")". 170 171expr(+X) --> p "+ ", expr(X), ")". 172expr(-X) --> p "- ", expr(X), ")". 173expr(X+Y) --> p expr(X), " + ", expr(Y). 174expr(X-Y) --> p expr(X), " + ", expr(Y). 175expr(X*Y) --> p expr(X), " * ", expr(Y). 176expr(X/Y) --> p expr(X), " / ", expr(Y). 177expr(X) --> {number(X)}, at(X). 178expr(X) --> object(X). 179 180resource(R) --> variable(R). 181resource(R) --> {rdf_global_id(R,RR)}, uri(RR). 182 183object(literal(Lit)) --> literal(Lit). 184object(Resource) --> resource(Resource). 185 186literal(lang(Lang,Val)) --> quote(at(Val)), "@", at(Lang). 187literal(type(Type,Val)) --> quote(wr(Val)), "^^", resource(Type). 188literal(Lit) --> {atomic(Lit)}, quote(at(Lit)). 189 190uri(U) --> {atom(U)}, "<", at(U), ">". 191quote(P) --> "\"", escape_with(0'\\,0'",P), "\"". 192variable(V) --> {var_number(V,N)}, "?v", at(N). 193variable(@V) --> "_:", {atomic(V) -> N=V; var_number(V,N)}, at(N). 194variable(@) --> "[]"