/* Part of SWI-Prolog Author: Jan Wielemaker E-mail: J.Wielemaker@uva.nl WWW: http://www.swi-prolog.org Copyright (C): 2002-2010, University of 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 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(rdf_triple, [ rdf_triples/2, % +Parsed, -Tripples rdf_triples/3, % +Parsed, -Tripples, +Tail rdf_reset_ids/0, % Reset gensym id's rdf_start_file/2, % +Options, -Cleanup rdf_end_file/1, % +Cleanup anon_prefix/1 % Prefix for anonynmous resources ]). :- use_module(library(gensym)). :- use_module(rdf_parser). /** Create triples from intermediate representation Convert the output of xml_to_rdf/3 from library(rdf) into a list of triples of the format described below. The intermediate representation should be regarded a proprietary representation. rdf(Subject, Predicate, Object). Where `Subject' is * Atom The subject is a resource * each(URI) URI is the URI of an RDF Bag * prefix(Pattern) Pattern is the prefix of a fully qualified Subject URI And `Predicate' is * Atom The predicate is always a resource And `Object' is * Atom URI of Object resource * literal(Value) Literal value (Either a single atom or parsed XML data) */ %% rdf_triples(+Term, -Triples) is det. %% rdf_triples(+Term, -Tridpples, +Tail) is det. % % Convert an object as parsed by rdf.pl into a list of rdf/3 % triples. The identifier of the main object created is returned % by rdf_triples/3. % % Input is the `content' of the RDF element in the format as % generated by load_structure(File, Term, [dialect(xmlns)]). % rdf_triples/3 can process both individual descriptions as % well as the entire content-list of an RDF element. The first % mode is suitable when using library(sgml) in `call-back' mode. rdf_triples(RDF, Tripples) :- rdf_triples(RDF, Tripples, []). rdf_triples([]) --> !, []. rdf_triples([H|T]) --> !, rdf_triples(H), rdf_triples(T). rdf_triples(Term) --> triples(Term, _). %% triples(-Triples, -Id, +In, -Tail) % % DGC set processing the output of xml_to_rdf/3. Id is unified to % the identifier of the main description. triples(description(Type, About, Props), Subject) --> { var(About), share_blank_nodes(true) }, !, ( { shared_description(description(Type, Props), Subject) } -> [] ; { make_id('__Description', Id) }, triples(description(Type, about(Id), Props), Subject), { assert_shared_description(description(Type, Props), Subject) } ). triples(description(description, IdAbout, Props), Subject) --> !, { description_id(IdAbout, Subject) }, properties(Props, Subject). triples(description(TypeURI, IdAbout, Props), Subject) --> { description_id(IdAbout, Subject) }, properties([ rdf:type = TypeURI | Props ], Subject). triples(unparsed(Data), Id) --> { make_id('__Error', Id), print_message(error, rdf(unparsed(Data))) }, []. /******************************* * DESCRIPTIONS * *******************************/ :- thread_local node_id/2, % nodeID --> ID unique_id/1. % known rdf:ID rdf_reset_node_ids :- retractall(node_id(_,_)), retractall(unique_id(_)). description_id(Id, Id) :- var(Id), !, make_id('__Description', Id). description_id(about(Id), Id). description_id(id(Id), Id) :- ( unique_id(Id) -> print_message(error, rdf(redefined_id(Id))) ; assert(unique_id(Id)) ). description_id(each(Id), each(Id)). description_id(prefix(Id), prefix(Id)). description_id(node(NodeID), Id) :- ( node_id(NodeID, Id) -> true ; make_id('__Node', Id), assert(node_id(NodeID, Id)) ). properties(PlRDF, Subject) --> properties(PlRDF, 1, [], [], Subject). properties([], _, Bag, Bag, _) --> []. properties([H0|T0], N, Bag0, Bag, Subject) --> property(H0, N, NN, Bag0, Bag1, Subject), properties(T0, NN, Bag1, Bag, Subject). %% property(Property, N, NN, Subject)// is det. % % Generate triples for {Subject, Pred, Object}. Also generates % triples for Object if necessary. % % @param Property One of % % * Pred = Object % Used for normal statements % * id(Id, Pred = Object) % Used for reified statements property(Pred0 = Object, N, NN, BagH, BagT, Subject) --> % inlined object triples(Object, Id), !, { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, Id, _, BagH, BagT). property(Pred0 = collection(Elems), N, NN, BagH, BagT, Subject) --> !, { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, Object, _Id, BagH, BagT), collection(Elems, Object). property(Pred0 = Object, N, NN, BagH, BagT, Subject) --> !, { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, Object, _Id, BagH, BagT). property(id(Id, Pred0 = Object), N, NN, BagH, BagT, Subject) --> triples(Object, ObjectId), !, { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, ObjectId, Id, BagH, BagT). property(id(Id, Pred0 = collection(Elems)), N, NN, BagH, BagT, Subject) --> !, { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, Object, Id, BagH, BagT), collection(Elems, Object). property(id(Id, Pred0 = Object), N, NN, BagH, BagT, Subject) --> { li_pred(Pred0, Pred, N, NN) }, statement(Subject, Pred, Object, Id, BagH, BagT). %% statement(+Subject, +Pred, +Object, +Id, +BagH, -BagT) % % Add a statement to the model. If nonvar(Id), we reinify the % statement using the given Id. statement(Subject, Pred, Object, Id, BagH, BagT) --> rdf(Subject, Pred, Object), { BagH = [Id|BagT] -> statement_id(Id) ; BagT = BagH }, ( { nonvar(Id) } -> rdf(Id, rdf:type, rdf:'Statement'), rdf(Id, rdf:subject, Subject), rdf(Id, rdf:predicate, Pred), rdf(Id, rdf:object, Object) ; [] ). statement_id(Id) :- nonvar(Id), !. statement_id(Id) :- make_id('__Statement', Id). %% li_pred(+Pred, -Pred, +Nth, -NextNth) % % Transform rdf:li predicates into _1, _2, etc. li_pred(rdf:li, rdf:Pred, N, NN) :- !, NN is N + 1, atom_concat('_', N, Pred). li_pred(Pred, Pred, N, N). %% collection(+Elems, -Id) % % Handle the elements of a collection and return the identifier % for the whole collection in Id. collection([], Nil) --> { global_ref(rdf:nil, Nil) }. collection([H|T], Id) --> triples(H, HId), { make_id('__List', Id) }, rdf(Id, rdf:type, rdf:'List'), rdf(Id, rdf:first, HId), rdf(Id, rdf:rest, TId), collection(T, TId). rdf(S0, P0, O0) --> { global_ref(S0, S), global_ref(P0, P), global_obj(O0, O) }, [ rdf(S, P, O) ]. global_ref(In, Out) :- ( nonvar(In), In = NS:Local -> ( NS == rdf, rdf_name_space(RDF) -> atom_concat(RDF, Local, Out) ; atom_concat(NS, Local, Out) ) ; Out = In ). global_obj(V, V) :- var(V), !. global_obj(literal(type(Local, X)), literal(type(Global, X))) :- !, global_ref(Local, Global). global_obj(literal(X), literal(X)) :- !. global_obj(Local, Global) :- global_ref(Local, Global). /******************************* * SHARING * *******************************/ :- thread_local shared_description/3, % +Hash, +Term, -Subject share_blank_nodes/1, % Boolean shared_nodes/1. % counter reset_shared_descriptions :- retractall(shared_description(_,_,_)), retractall(shared_nodes(_)). shared_description(Term, Subject) :- term_hash(Term, Hash), shared_description(Hash, Term, Subject), ( retract(shared_nodes(N)) -> N1 is N + 1 ; N1 = 1 ), assert(shared_nodes(N1)). assert_shared_description(Term, Subject) :- term_hash(Term, Hash), assert(shared_description(Hash, Term, Subject)). /******************************* * START/END * *******************************/ %% rdf_start_file(+Options, -Cleanup) is det. % % Initialise for the translation of a file. rdf_start_file(Options, Cleanup) :- rdf_reset_node_ids, % play safe reset_shared_descriptions, set_bnode_sharing(Options, C1), set_anon_prefix(Options, C2), add_cleanup(C1, C2, Cleanup). %% rdf_end_file(:Cleanup) is det. % % Cleanup reaching the end of an RDF file. rdf_end_file(Cleanup) :- rdf_reset_node_ids, ( shared_nodes(N) -> print_message(informational, rdf(shared_blank_nodes(N))) ; true ), reset_shared_descriptions, Cleanup. set_bnode_sharing(Options, erase(Ref)) :- option(blank_nodes(Share), Options, noshare), ( Share == share -> assert(share_blank_nodes(true), Ref), ! ; Share == noshare -> fail % next clause ; throw(error(domain_error(share, Share), _)) ). set_bnode_sharing(_, true). set_anon_prefix(Options, erase(Ref)) :- option(base_uri(BaseURI), Options), nonvar(BaseURI), !, atomic_list_concat(['__', BaseURI, '#'], AnonBase), asserta(anon_prefix(AnonBase), Ref). set_anon_prefix(_, true). add_cleanup(true, X, X) :- !. add_cleanup(X, true, X) :- !. add_cleanup(X, Y, (X, Y)). /******************************* * UTIL * *******************************/ %% anon_prefix(-Prefix) is semidet. % % If defined, it is the prefix used to generate a blank node. :- thread_local anon_prefix/1. make_id(For, ID) :- anon_prefix(Prefix), !, atom_concat(Prefix, For, Base), gensym(Base, ID). make_id(For, ID) :- gensym(For, ID). anon_base('__Description'). anon_base('__Statement'). anon_base('__List'). anon_base('__Node'). %% rdf_reset_ids is det. % % Utility predicate to reset the gensym counters for the various % generated identifiers. This simplifies debugging and matching % output with the stored desired output (see rdf_test.pl). rdf_reset_ids :- anon_prefix(Prefix), !, ( anon_base(Base), atom_concat(Prefix, Base, X), reset_gensym(X), fail ; true ). rdf_reset_ids :- ( anon_base(Base), reset_gensym(Base), fail ; true ).