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yap-6.3/packages/semweb/rdf_turtle_write.pl

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semweb and http compile now (but they don't work properly yet).
2010-07-15 23:35:37 +01:00
/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 2009, 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_turtle_write,
[ rdf_save_turtle/2, % +File, +Options
rdf_save_canonical_turtle/2 % +File, +Options
]).
:- use_module(library(semweb/rdf_db)).
:- use_module(library(semweb/turtle_base)).
:- use_module(library(option)).
:- use_module(library(record)).
:- use_module(library(error)).
:- use_module(library(lists)).
:- use_module(library(rbtrees)).
:- use_module(library(apply)).
:- use_module(library(url)).
:- use_module(library(pairs)).
:- use_module(library(debug)).
:- use_module(library(sgml_write)).
/** <module> Turtle - Terse RDF Triple Language writer
This module implements the Turtle language for representing the RDF
triple model as defined by Dave Beckett from the Institute for Learning
and Research Technology University of Bristol in the document:
* http://www.w3.org/TeamSubmission/turtle/
* http://www.w3.org/TeamSubmission/2008/SUBM-turtle-20080114/#sec-conformance
The Turtle format is designed as an RDF serialization that is easy to
read and write by both machines and humans. Due to the latter property,
this library goes a long way in trying to produce human-readable output.
In addition to the human-readable format, this library can write a
_canonical_ representation of RDF graphs. The canonical representation
has the following properties:
* Equivalent graphs result in the same document. Graphs are
considered equivalent iff they contain the same _set_ of
triples, regardless of the labeling of blank nodes in the
graph.
* Changes to the graph are diff-friendly. This means
- Prefixes are combined in the header and thus changes
to the namespaces only result in changes in the header.
- Blank nodes that are used only once (including collections)
are written in-line with the object they belong to.
- For other blank nodes we to realise stable labeling that
is based on property-values.
@tbd Low-level string output takes 28% of the time. Move to C?
*/
:- record
tw_state(graph, % graph being saved
base, % The base-URI
encoding=utf8, % Desired encoding
indent:nonneg=8, % Indent for ; and ,-lists
tab_distance:nonneg=8, % Tab distance
subject_white_lines:nonneg=1,%Extra lines between subjects
align_prefixes:boolean=true,%Align prefix declarations
user_prefixes:boolean=true,% Use rdf_current_ns/2?
comment:boolean=true, % write some comments into the file
group:boolean=true, % Group using ; and ,
single_line_bnodes:boolean=false, % No newline after ;
canonize_numbers:boolean=false, % How to write numbers
canonical:boolean=false,
% Private fields
bnode_id=0, % Incrementing bnode-id
nodeid_map, % RBTree mapping NodeIDs to Refs
bnode_hash, % RBTree holding reuse-count of hashes
subject_count, % # subjects saved
triple_count=0, % # triples saved
base_root, % Root URL of base
base_dir, % Directory
base_path, % Path of base
prefix_map). % List of Prefix-Map
%% rdf_save_turtle(+Out, +Options) is det.
%
% Save an RDF graph as N3. Options processed are:
%
% * align_prefixes(+Boolean)
% Nicely align the @prefix declarations
% * base(+Base)
% Save relative to the given Base
% * canonize_numbers(+Boolean)
% If =true= (default =false=), emit numeric datatypes using
% Prolog's write to achieve canonical output.
% * comment(+Boolean)
% It =true= (default), write some informative comments
% between the output segments
% * encoding(+Encoding)
% Encoding used for the output stream. Default is UTF-8.
% * indent(+Column)
% Indentation for ; -lists. `0' does not indent, but
% writes on the same line. Default is 8.
% * graph(+Graph)
% Save only the named graph
% * group(+Boolean)
% If =true= (default), using P-O and O-grouping.
% * single_line_bnodes(+Bool)
% If =true= (default =false=), write [...] and (...) on a
% single line.
% * subject_white_lines(+Count)
% Extra white lines to insert between statements about a
% different subject. Default is 1.
% * tab_distance(+Tab)
% Distance between tab-stops. `0' forces the library to
% use only spaces for layout. Default is 8.
% * user_prefixes(+Boolean)
% If =true= (default), use prefixes from rdf_current_ns/2.
%
% @param Out is one of stream(Stream), a stream handle, a file-URL
% or an atom that denotes a filename.
rdf_save_turtle(Spec, Options) :-
thread_self(Me),
thread_statistics(Me, cputime, T0),
must_be(list, Options),
make_tw_state(Options, State0, _Rest),
init_base(State0, State1),
init_prefix_map(State1, State),
tw_state_encoding(State, Enc),
open_output(Spec, Enc, Stream, Cleanup),
call_cleanup(tw_graph(State, Stream),
Cleanup),
thread_statistics(Me, cputime, T1),
Time is T1-T0,
tw_state_triple_count(State, SavedTriples),
tw_state_subject_count(State, SavedSubjects),
print_message(informational,
rdf(saved(Spec, Time, SavedSubjects, SavedTriples))).
%% rdf_save_canonical_turtle(+Spec, +Options) is det.
%
% Save triples in a canonical format. This is the same as
% rdf_save_turtle/3, but using different defaults. In particular:
%
% * encoding(utf8),
% * indent(0),
% * tab_distance(0),
% * subject_white_lines(1),
% * align_prefixes(false),
% * user_prefixes(false)
% * comment(false),
% * group(false),
% * single_line_bnodes(true)
%
% @tbd Work in progress. Notably blank-node handling is
% incomplete.
rdf_save_canonical_turtle(Spec, Options) :-
rdf_save_turtle(Spec,
[ encoding(utf8),
indent(0),
tab_distance(0),
subject_white_lines(1),
align_prefixes(false),
user_prefixes(false),
comment(false),
group(false),
single_line_bnodes(true),
canonical(true)
| Options
]).
%% open_output(+Spec, +Encoding, -Stream, -Cleanup) is det.
%
% Open output Spec, returning a stream using Encoding.
%
% @param Cleanup is a goal that must be used to revert the side
% effects of open_output/4.
open_output(stream(Out), Encoding, Out,
set_stream(Out, encoding(Old))) :- !,
stream_property(Out, encoding(Old)),
set_stream(Out, encoding(Encoding)).
open_output(Stream, Encoding, Out, Cleanup) :-
\+ atom(Stream),
is_stream(Stream), !,
open_output(stream(Stream), Encoding, Out, Cleanup).
open_output(Spec, Encoding, Out,
close(Out)) :-
out_to_file(Spec, File),
open(File, write, Out, [encoding(Encoding)]).
out_to_file(URL, File) :-
atom(URL),
file_name_to_url(File, URL), !.
out_to_file(File, File).
/*******************************
* PREFIXES *
*******************************/
%% init_prefix_map(+State, -State) is det.
%
% Set the prefix_map of State. The prefix map is list of
% Prefix-URI of prefixes to use for emitting the graph requested
% in State. If multiple prefixes are present where the one is a
% prefix of the other, the longer one appears first in the list.
init_prefix_map(State0, State) :-
tw_state_graph(State0, Graph),
rdf_graph_prefixes(Graph, Prefixes, turtle_prefix),
remove_base(State0, Prefixes, Prefixes2),
prefix_names(Prefixes2, State0, Pairs),
transpose_pairs(Pairs, URI_Abrevs),
reverse(URI_Abrevs, RURI_Abrevs),
flip_pairs(RURI_Abrevs, PrefixMap),
set_prefix_map_of_tw_state(PrefixMap, State0, State).
%% turtle_prefix(+Where, +Prefix, +URI) is semidet.
%
% Test whether we want to include the proposed prefix in the
% @prefix declaration.
turtle_prefix(_, Prefix, URI) :-
sub_atom(Prefix, _, 1, 0, Last),
turtle_prefix_char(Last),
atom_concat(Prefix, Local, URI),
\+ sub_atom(Local, _, _, _, '.').
turtle_prefix_char('#').
turtle_prefix_char('/').
remove_base(State, Prefixes, PrefixesNoBase) :-
tw_state_base_dir(State, BaseDir),
atom(BaseDir), !,
delete(Prefixes, BaseDir, PrefixesNoBase).
remove_base(_State, Prefixes, Prefixes).
flip_pairs([], []).
flip_pairs([Key-Val|Pairs], [Val-Key|Flipped]) :-
flip_pairs(Pairs, Flipped).
prefix_names(URIs, State, Prefixes) :-
prefix_names(URIs, State, 1, Prefixes, []).
prefix_names([], _, _, List, List) :- !.
prefix_names(URIs, State, Len, Prefixes, Tail) :-
prefix_names(URIs, State, Len, Prefixes, PTail, Rest),
Len1 is Len + 1,
prefix_names(Rest, State, Len1, PTail, Tail).
prefix_names(URIs, State, Len, Prefixes, PTail, Rest) :-
map_list_to_pairs(propose_abbrev(State, Len), URIs, Pairs), !,
keysort(Pairs, Sorted),
unique(Sorted, Prefixes, PTail, Rest).
prefix_names(URIs, _, _, Prefixes, PTail, []) :-
number_prefixes(URIs, 1, Prefixes, PTail).
number_prefixes([], _, PL, PL).
number_prefixes([H|T0], N, [P-H|PL], T) :-
atomic_concat(ns, N, P),
succ(N, N1),
number_prefixes(T0, N1, PL, T).
unique([], L, L, []).
unique([A-U|T0], [A-U|T], L, Rest) :-
T0 \= [A-_|_], !,
unique(T0, T, L, Rest).
unique([A-U|T0], Prefixes, L, [U|Rest0]) :-
strip_keys(T0, A, T1, Rest0, Rest),
unique(T1, Prefixes, L, Rest).
strip_keys([A-U|T0], A, T, [U|R0], R) :- !,
strip_keys(T0, A, T, R0, R).
strip_keys(L, _, L, R, R).
%% propose_abbrev(+State, +Len, +URI, -Abbrev) is multi.
%
% Propose an abbreviation for URI. Backtracking yields longer
% ones.
propose_abbrev(_, _, URI, Abbrev) :-
well_known_ns(Abbrev, URI), !.
propose_abbrev(State, _, URI, Abbrev) :-
tw_state_user_prefixes(State, true),
rdf_current_ns(Abbrev, URI), !.
propose_abbrev(_, Len, URI, Abbrev) :-
namespace_parts(URI, Parts),
include(abbrev_part, Parts, Names),
reverse(Names, RevNames),
length(Use, Len),
append(Use, _, RevNames),
atomic_list_concat(Use, -, Abbrev).
abbrev_part(X) :-
turtle_name(X),
\+ well_known_ns(X, _),
\+ well_known_extension(X).
well_known_ns(rdf, 'http://www.w3.org/1999/02/22-rdf-syntax-ns#').
well_known_ns(rdfs, 'http://www.w3.org/2000/01/rdf-schema#').
well_known_ns(owl, 'http://www.w3.org/2002/07/owl#').
well_known_ns(xsd, 'http://www.w3.org/2001/XMLSchema#').
well_known_ns(dc, 'http://purl.org/dc/elements/1.1/').
well_known_extension(ttl).
well_known_extension(nt).
well_known_extension(n3).
well_known_extension(xml).
well_known_extension(rdf).
well_known_extension(owl).
%% namespace_parts(+URL, -Parts)
namespace_parts(URL, Parts) :-
atom_codes(URL, Codes),
phrase(parts(Parts), Codes), !.
namespace_parts(URL, _) :-
format(user_error, 'Couldn\'t split ~q~n', [URL]),
fail.
parts(List) --> sep2, parts2(List).
parts2([H|T]) -->
string(Codes), {Codes \== []},
sep, !,
{atom_codes(H, Codes)},
parts2(T).
parts2([]) --> [].
string([]) --> [].
string([H|T]) --> [H], string(T).
sep --> sep_char, sep2.
sep([], []).
sep2 --> sep_char, !, sep2.
sep2 --> [].
sep_char --> "/".
sep_char --> ":".
sep_char --> ".".
sep_char --> "?".
sep_char --> "#".
%% init_base(+State0, -State) is det.
%
% Initialise dealing with the base URI. It sets two attributes of
% the state: base_root and base_path.
init_base(State0, State) :-
tw_state_base(State0, BaseURI),
atom(BaseURI), !,
parse_url(BaseURI, Attributes),
include(root_part, Attributes, RootAttrs),
parse_url(BaseRoot, RootAttrs),
memberchk(path(BasePath), Attributes),
file_directory_name(BasePath, BaseDir),
atomic_list_concat([BaseRoot, BaseDir, /], BaseDirURI),
set_base_root_of_tw_state(BaseRoot, State0, State1),
set_base_path_of_tw_state(BasePath, State1, State2),
set_base_dir_of_tw_state(BaseDirURI, State2, State).
init_base(State, State).
root_part(protocol(_)).
root_part(host(_)).
root_part(port(_)).
/*******************************
* SAVE *
*******************************/
%% tw_graph(+State, +Out) is det.
%
% Write an RDF graph as Turtle data.
%
% @tbd Write unconnected and multi-connected blank-nodes.
tw_graph(State, Out) :-
tw_state_prefix_map(State, PrefixMap),
tw_prefix_map(PrefixMap, State, Out),
subjects(State, Subjects),
length(Subjects, SubjectCount),
tw_state_subject_count(State, SubjectCount),
partition(rdf_is_bnode, Subjects, BNodes, ProperSubjects),
maplist(pair_var, BNodes, Pairs),
ord_list_to_rbtree(Pairs, BNTree),
tw_state_nodeid_map(State, BNTree),
( ProperSubjects == []
-> true
; length(ProperSubjects, PSCount),
comment(State, 'Named toplevel resources (~D)', [PSCount], Out),
tw_proper_subjects(ProperSubjects, State, Out)
),
tw_bnodes(Pairs, State, Out).
pair_var(BNode, BNode-_).
%% tw_prefix_map(+PrefixMap, +State, +Out) is det.
%
% Write the @base and @prefix declarations
tw_prefix_map(PrefixMap, State, Out) :-
tw_state_align_prefixes(State, true), !,
longest_prefix(PrefixMap, 0, Length),
PrefixCol is Length+10,
tw_base(PrefixCol, State, Out),
tw_prefix_map(PrefixMap, PrefixCol, State, Out).
tw_prefix_map(PrefixMap, State, Out) :-
tw_base(0, State, Out),
tw_prefix_map(PrefixMap, 0, State, Out).
longest_prefix([], L, L).
longest_prefix([Prefix-_|T], L0, L) :-
atom_length(Prefix, L1),
L2 is max(L0, L1),
longest_prefix(T, L2, L).
tw_base(Col, State, Out) :-
tw_state_base(State, Base),
atom(Base), !,
format(Out, '@base ~t~*|', [Col]),
turtle_write_uri(Out, Base),
format(Out, ' .~n', []).
tw_base(_, _, _).
tw_prefix_map([], _, _, _).
tw_prefix_map([Prefix-URI|T], Col, State, Out) :-
format(Out, '@prefix ~t~w: ~*|', [Prefix, Col]),
tw_relative_uri(URI, State, Out),
format(Out, ' .~n', []),
( T == []
-> true
; tw_prefix_map(T, Col, State, Out)
).
%% tw_proper_subjects(+Subjects, +State, +Out) is det.
%
% Write the subjects that are not Bnodes.
tw_proper_subjects([], _, _).
tw_proper_subjects([H|T], State, Out) :-
separate_subjects(State, Out),
tw_subject(H, H, State, Out),
tw_proper_subjects(T, State, Out).
separate_subjects(State, Out) :-
tw_state_subject_white_lines(State, ExtraLines),
put_n(ExtraLines, '\n', Out).
%% tw_subject(+URI, +State, +Out) is det.
%
% Write a toplevel non-bnode subject.
tw_subject(URI, Ref, State, Out) :-
subject_triples(URI, State, Pairs),
length(Pairs, Count),
inc_triple_count(State, Count),
group_po(Pairs, Grouped),
tw_subject_triples(Grouped, Ref, State, Out).
group_po(Pairs, Grouped) :-
group_pairs_by_key(Pairs, Grouped0),
rdf_equal(rdf:type, RDFType),
( select(RDFType-Types, Grouped0, Grouped1)
-> Grouped = [RDFType-Types|Grouped1]
; Grouped = Grouped0
).
%% tw_bnodes(+Pairs, +State, +Out) is det.
%
% Write the Bnodes. Pairs is a list URI-Ref, where Ref is one of
% =written= if the Bnode is already written; an integer if it is
% used multiple times or a variable if it has not been written.
% The order in which we deal with bnodes is defined as follows:
%
% * First, write the bnodes that are not referenced at all
% as toplevel bnodes using [ ... ] notation.
%
% * Next, write the bnodes that need written as toplevel
% nodes using the _:XX notation because they are referenced
% multiple times in the graph. Continue this process until it
% is exhausted.
tw_bnodes(Pairs, State, Out) :-
tw_top_bnodes(Pairs, State, Out, Rest1),
tw_numbered_bnodes(Rest1, State, Out, 1, Rest2),
tw_cyclic_bnodes(Rest2, State, Out, 0).
tw_numbered_bnodes([], _, _, _, []) :- !.
tw_numbered_bnodes(Pairs, State, Out, Level, Rest) :-
multi_referenced(Pairs, RefPairs, Rest0),
( RefPairs == []
-> Rest = Rest0
; length(RefPairs, Count),
comment(State, 'Level ~D multi-referenced blank-nodes (~D)',
[ Level, Count ], Out),
tw_ref_bnodes(RefPairs, State, Out),
Level1 is Level + 1,
tw_numbered_bnodes(Rest0, State, Out, Level1, Rest)
).
multi_referenced([], [], []).
multi_referenced([H|T], RefPairs, Rest) :-
H = _-Ref,
( Ref == written
-> multi_referenced(T, RefPairs, Rest)
; var(Ref)
-> Rest = [H|TR],
multi_referenced(T, RefPairs, TR)
; assertion(Ref = bnode(_)),
RefPairs = [H|TRP], % assigned reference
multi_referenced(T, TRP, Rest)
).
tw_ref_bnodes([], _, _).
tw_ref_bnodes([BNode-Ref|T], State, Out) :-
separate_subjects(State, Out),
tw_subject(BNode, Ref, State, Out),
tw_ref_bnodes(T, State, Out).
%% tw_top_bnodes(+Pairs, +State, +Out, -Rest)
%
% Write the top bnodes: those that do not appear as an object
% anywhere.
tw_top_bnodes(Pairs, State, Out, Rest) :-
unreferenced(Pairs, State, TopBNodes, Rest),
( TopBNodes == []
-> true
; length(TopBNodes, Count),
comment(State, 'Toplevel blank-nodes (~D)', [Count], Out),
sort_bnodes(TopBNodes, SortedTopBNodes, State),
tw_top_bnodes(SortedTopBNodes, State, Out)
).
unreferenced([], _, [], []).
unreferenced([H|T], State, UnrefPairs, Rest) :-
H = BNode-Ref,
( Ref == written
-> unreferenced(T, State, UnrefPairs, Rest)
; var(Ref),
object_link_count(BNode, State, 0)
-> UnrefPairs = [H|URT],
unreferenced(T, State, URT, Rest)
; Rest = [H|TR],
unreferenced(T, State, UnrefPairs, TR)
).
tw_top_bnodes([], _, _).
tw_top_bnodes([BNode-_|T], State, Out) :-
tw_bnode(BNode, State, Out),
tw_top_bnodes(T, State, Out).
tw_bnode(BNode, State, Out) :-
subject_triples(BNode, State, Pairs),
tw_bnode_triples(Pairs, State, Out),
format(Out, ' .~n', []).
tw_bnode_triples(Pairs, State, Out) :-
length(Pairs, Count),
inc_triple_count(State, Count),
group_po(Pairs, Grouped),
( tw_state_single_line_bnodes(State, true)
-> format(Out, '[ ', []),
tw_triples(Grouped, -1, State, Out),
format(Out, ' ]', [])
; line_position(Out, Indent),
format(Out, '[ ', []),
line_position(Out, AIndent),
tw_triples(Grouped, AIndent, State, Out),
nl_indent(Out, State, Indent),
format(Out, ']', [])
).
%% tw_cyclic_bnodes(+Pairs, +BNode, +State, +Out, +Cycle)
%
% The rest. These are groups of bnodes that are reachable, but we
% cannot find a starting point, neither from a named resource, nor
% from an unlinked bnode. As long as we are not considering stable
% canonical output, we can break the cycle at any point.
tw_cyclic_bnodes([], _State, _Out, _) :- !.
tw_cyclic_bnodes(Pairs, State, Out, Cycle0) :-
( tw_state_canonical(State, true)
-> sort_bnode_pairs(Pairs, BNodes, State)
; BNodes = Pairs
),
succ(Cycle0, Cycle),
BNodes = [BNode-Ref|_],
next_bnode_id(State, BNode, Ref),
comment(State, 'Breaking cycle ~D', [Cycle], Out),
tw_numbered_bnodes(Pairs, State, Out, 1, Rest),
tw_cyclic_bnodes(Rest, State, Out, Cycle).
%% tw_subject_triples(+Grouped, +Subject, +State, +Out)
%
% Save triples on Subject. Combine groups of triples with the
% same subject (;) and same subject+predicate (,).
%
% @param Subject is either a URI or an integer. The latter is
% used for writing a named bnode.
tw_subject_triples([], _, _, _) :- !.
tw_subject_triples(Grouped, URI, State, Out) :-
tw_state_group(State, false), !,
tw_ungrouped_triples(Grouped, URI, State, Out).
tw_subject_triples(Grouped, URI, State, Out) :-
tw_resource(URI, State, Out),
( tw_state_indent(State, Indent),
Indent > 0
-> nl_indent(Out, State, Indent)
; put_char(Out, ' '),
line_position(Out, Indent)
),
tw_triples(Grouped, Indent, State, Out),
format(Out, ' .~n', []).
%% tw_ungrouped_triples(+Grouped, +URI, +State, +Out)
%
% Write triples for subject URI as one line per triple. Used
% for canonical output.
tw_ungrouped_triples([], _, _, _).
tw_ungrouped_triples([P-Vs|Groups], URI, State, Out) :-
partition(rdf_is_bnode, Vs, BNVs, ProperVs),
tw_ungrouped_values(ProperVs, P, URI, State, Out),
sort_bnodes(BNVs, SortedBNVs, State),
tw_ungrouped_values(SortedBNVs, P, URI, State, Out),
tw_ungrouped_triples(Groups, URI, State, Out).
tw_ungrouped_values([], _, _, _, _).
tw_ungrouped_values([V|T], P, URI, State, Out) :-
tw_resource(URI, State, Out),
put_char(Out, ' '),
tw_predicate(P, State, Out),
put_char(Out, ' '),
tw_object(V, State, Out),
format(Out, ' .~n', []),
tw_ungrouped_values(T, P, URI, State, Out).
%% tw_triples(+Groups, +Indent, +State, +Out) is det.
%
% Triple writer that uses ; and ,- grouping
tw_triples([P-Vs|MoreGroups], Indent, State, Out) :-
tw_write_pvs(Vs, P, State, Out),
( MoreGroups == []
-> true
; format(Out, ' ;', []),
nl_indent(Out, State, Indent),
tw_triples(MoreGroups, Indent, State, Out)
).
tw_write_pvs(Values, P, State, Out) :-
tw_predicate(P, State, Out),
put_char(Out, ' '),
line_position(Out, Indent),
tw_write_vs(Values, Indent, State, Out).
tw_predicate(P, State, Out) :-
( rdf_equal(P, rdf:type)
-> format(Out, 'a', [])
; tw_resource(P, State, Out)
).
tw_write_vs([H|T], Indent, State, Out) :-
tw_object(H, State, Out),
( T == []
-> true
; format(Out, ' ,', []),
nl_indent(Out, State, Indent),
tw_write_vs(T, Indent, State, Out)
).
%% tw_object(+Value, +State, +Out) is det.
%
% Write the object of a triple.
tw_object(Value, State, Out) :-
rdf_is_bnode(Value), !,
tw_bnode_object(Value, State, Out).
tw_object(Value, State, Out) :-
atom(Value), !,
tw_resource(Value, State, Out).
tw_object(Literal, State, Out) :-
tw_literal(Literal, State, Out).
%% tw_bnode_object(+Value, +State, +Out) is det.
%
% Write a Bnode value. There are a number of cases:
%
% * The BNode was already written. Write the same ref.
% * The BNode is not shared. Inline and set =written=
% * The BNode is shared. Generate a NodeID and store it
% * The BNode is once as object: Generate a NodeID
% * The BNode is more than once object: Generate a NodeID
% and put in table.
tw_bnode_object(BNode, State, Out) :-
tw_state_nodeid_map(State, BNTree),
rb_lookup(BNode, Ref, BNTree), !,
( var(Ref)
-> ( tw_unshared_bnode(BNode, State, Out)
-> Ref = written
; next_bnode_id(State, BNode, Ref),
tw_bnode_ref(Ref, Out)
)
; tw_bnode_ref(Ref, Out)
).
tw_bnode_object(BNode, State, Out) :-
object_link_count(BNode, State, N),
N > 1, !,
tw_state_nodeid_map(State, BNTree0),
rb_insert(BNTree0, BNode, Ref, BNTree),
set_nodeid_map_of_tw_state(BNTree, State),
next_bnode_id(State, BNode, Ref),
tw_bnode_ref(Ref, Out).
tw_bnode_object(BNode, State, Out) :-
next_bnode_id(State, BNode, Ref),
tw_bnode_ref(Ref, Out).
tw_bnode_ref(bnode(Ref), Out) :-
( integer(Ref)
-> format(Out, '_:bn~w', [Ref])
; format(Out, '_:~w', [Ref])
).
%% tw_unshared_bnode(+BNode, +State, +Out) is semidet.
%
% Write a bnode if this is the only place it is used.
tw_unshared_bnode(BNode, State, Out) :-
object_link_count(BNode, State, 1),
subject_triples(BNode, State, Pairs),
( Pairs == []
-> format(Out, '[]', [])
; pairs_unshared_collection(Pairs, State, Collection)
-> ( Collection == []
-> format(Out, '()', [])
; tw_state_nodeid_map(State, BNTree),
rb_lookup(BNode, written, BNTree),
length(Collection, NMembers),
Triples is 2*NMembers,
inc_triple_count(State, Triples),
( tw_state_single_line_bnodes(State, true)
-> format(Out, '( ', []),
tw_collection(Collection, -1, State, Out),
format(Out, ' )', [])
; line_position(Out, Indent),
format(Out, '( ', []),
line_position(Out, AIndent),
tw_collection(Collection, AIndent, State, Out),
nl_indent(Out, State, Indent),
format(Out, ')', [])
)
)
; tw_bnode_triples(Pairs, State, Out)
).
tw_collection([H|T], Indent, State, Out) :-
tw_object(H, State, Out),
( T \== []
-> nl_indent(Out, State, Indent),
tw_collection(T, Indent, State, Out)
; true
).
%% unshared_collection(+URI, +State, -Members) is semidet.
%
% True if URI denodes an RDF list that is made up from bnodes, is
% linked exactly once to its context and contains no extra
% triples.
unshared_collection(C, _, []) :-
rdf_equal(C, rdf:nil), !.
unshared_collection(C, State, List) :-
rdf_is_bnode(C),
object_link_count(C, State, 1),
tw_state_nodeid_map(State, BNTree),
rb_lookup(C, written, BNTree),
subject_triples(C, State, Pairs),
pairs_unshared_collection(Pairs, State, List).
pairs_unshared_collection(Pairs, State, [H|T]) :-
rdf_equal(rdf:first, RDFFirst),
rdf_equal(rdf:rest, RDFRest),
Pairs = [ RDFFirst-H,
RDFRest-Rest
| More
],
( More == []
; rdf_equal(rdf:type, RDFType),
rdf_equal(rdf:'List', RDFList),
More == [RDFType-RDFList]
),
unshared_collection(Rest, State, T).
%% object_link_count(+BNode, +STate, -Count) is det.
%
% Number of times BNode is used as an object in the graph
object_link_count(BNode, State, Count) :-
tw_state_graph(State, Graph),
( var(Graph)
-> findall(S-P, rdf(S,P,BNode), Pairs0)
; findall(S-P, rdf(S,P,BNode,Graph), Pairs0)
),
sort(Pairs0, Pairs), % remove duplicates
length(Pairs, Count).
%% nl_indent(+Out, +State, +Indent) is det.
%
% Write a newline and indent to column Indent.
nl_indent(Out, _, -1) :- !,
put_char(Out, ' ').
nl_indent(Out, State, Indent) :-
nl(Out),
tw_state_tab_distance(State, TD),
( TD == 0
-> tab(Out, Indent)
; Tabs is Indent//TD,
Spaces is Indent mod TD,
put_n(Tabs, '\t', Out),
put_n(Spaces, ' ', Out)
).
put_n(N, Char, Out) :-
N > 0, !,
put_char(Out, Char),
N2 is N - 1,
put_n(N2, Char, Out).
put_n(_, _, _).
%% subject_triples(+URI, +State, -Pairs) is det.
%
% Pairs is a sorted list of P-O pairs representing all triples on
% the subject URI.
subject_triples(URI, State, Pairs) :-
tw_state_graph(State, Graph),
( var(Graph)
-> findall(P-O, rdf(URI, P, O), Pairs0)
; findall(P-O, rdf(URI, P, O, Graph), Pairs0)
),
sort(Pairs0, Pairs).
/*******************************
* GRAPH-LOGIC *
*******************************/
%% subjects(+State, -Subjects:ord_set) is det.
%
% Subjects is a list of all subjects in the graph requested in
% State.
subjects(State, Subjects) :-
findall(Subject, subject(State, Subject), AllSubjects),
sort(AllSubjects, Subjects).
subject(State, Subject) :-
tw_state_graph(State, Graph),
( atom(Graph)
-> rdf_subject(Subject),
( rdf(Subject, _, _, Graph)
-> true
)
; rdf_subject(Subject)
).
/*******************************
* CANONICAL ORDERING *
*******************************/
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
This section deals with the two problems of canonical graphs:
* Keep blank nodes in the same order
* Assign stable names to blank nodes that we need to
give a name. There are two cases: (1) a blank nodes is
used in more than one place and (2) a blank node series
is cyclic.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
%% sort_bnodes(+BNodes, -Sorted, +State) is det.
%
% Sort a list of blank nodes.
sort_bnodes(BNodes, Sorted, _State) :-
sort(BNodes, Sorted).
%% sort_bnode_pairs(+Pairs, -Sorted, +State) is det.
%
% Sort a list of Pairs BNode-Ref
sort_bnode_pairs(Pairs, Sorted, _State) :-
sort(Pairs, Sorted).
%% bnode_to_term(+BNode, -Term, +State)
%
% Term is a canonical representation of the graph formed by BNode.
% The transformation of a bnode is
%
% bnode(p-[o1,o2,..], ..)
%
% The arguments are alphabetically sorted on predicate (can't we
% leave the preds out them?) and the objects are alphabetically
% sorted. Sorting multiple bnode values?
%% next_bnode_id(+State, +BNode, -Ref) is det.
%
% Generate a node-id for BNode. When writing non-canonically, we
% simply number the bnodes. Otherwise we want a more stable
% numbering. Our numbering is a hash of the content of the bnode.
% It is not unlikely that we find muliple copies, and therefore we
% number the full id is bn_<hash>_<n>, <n> counting 0...
next_bnode_id(State, _BNode, bnode(Ref)) :-
tw_state_canonical(State, false), !,
tw_state_bnode_id(State, Ref0),
Ref is Ref0+1,
nb_set_bnode_id_of_tw_state(Ref, State).
next_bnode_id(State, BNode, bnode(Ref)) :-
bnode_hash(BNode, Hash),
tw_state_bnode_hash(State, BNHash),
( var(BNHash)
-> rb_empty(BNHash)
; true
),
( rb_update(BNHash, Hash, C0, C, BNHash1)
-> C is C0+1
; C = 0,
rb_insert(BNHash, Hash, C, BNHash1)
),
set_bnode_hash_of_tw_state(BNHash1, State),
format(atom(Ref), 'bn_~w_~d', [Hash, C]).
%% bnode_hash(+BNode, -Hash) is det.
%
% Hash is the hash-value for a bnode.
%
% @tbd: Hash on content.
bnode_hash(BNode, Hash) :-
term_hash(BNode, Hash).
/*******************************
* PRIMITIVES *
*******************************/
%% tw_resource(+Resource, +State, +Out) is det.
%
% Write a resource
tw_resource(BNodeID, _, Out) :-
BNodeID = bnode(_), !,
tw_bnode_ref(BNodeID, Out).
tw_resource(Resource, State, Out) :-
tw_state_prefix_map(State, PrefixMap),
member(Prefix-Full, PrefixMap),
atom_concat(Full, Name, Resource),
turtle_name(Name), !,
format(Out, '~w:~w', [Prefix, Name]).
tw_resource(Resource, State, Out) :-
tw_relative_uri(Resource, State, Out).
tw_relative_uri(Resource, State, Out) :-
tw_state_base_root(State, Root),
atom(Root),
atom_concat(Root, ResPath, Resource),
sub_atom(ResPath, 0, _, _, /),
tw_state_base_path(State, BasePath),
relative_path(ResPath, BasePath, RelPath), !,
turtle_write_uri(Out, RelPath).
tw_relative_uri(Resource, _, Out) :-
turtle_write_uri(Out, Resource).
relative_path(Path, RelTo, RelPath) :-
atomic_list_concat(PL, /, Path),
atomic_list_concat(RL, /, RelTo),
delete_common_prefix(PL, RL, PL1, PL2),
to_dot_dot(PL2, DotDot, PL1),
atomic_list_concat(DotDot, /, RelPath).
delete_common_prefix([H|T01], [H|T02], T1, T2) :- !,
delete_common_prefix(T01, T02, T1, T2).
delete_common_prefix(T1, T2, T1, T2).
to_dot_dot([], Tail, Tail).
to_dot_dot([_], Tail, Tail) :- !.
to_dot_dot([_|T0], ['..'|T], Tail) :-
to_dot_dot(T0, T, Tail).
%% tw_literal(+Literal, +State, +Out) is det.
%
% Write a literal value to the stream Out.
tw_literal(literal(type(Type, Value)), State, Out) :- !,
tw_typed_literal(Type, Value, State, Out).
tw_literal(literal(lang(Lang, Value)), State, Out) :- !,
tw_quoted_string(Value, State, Out),
downcase_atom(Lang, TurtleLang), % Turtle lang = [a-z]+('-'[a-z0-9]+)*
format(Out, '@~w', [TurtleLang]).
tw_literal(literal(Value), State, Out) :-
atom(Value), !,
tw_quoted_string(Value, State, Out).
tw_literal(literal(Value), State, Out) :-
atom(Value), !,
tw_quoted_string(Value, State, Out).
% Add types automatically
tw_literal(literal(Value), State, Out) :-
integer(Value), !,
rdf_equal(Type, xsd:integer),
tw_typed_literal(Type, Value, State, Out).
tw_literal(literal(Value), State, Out) :-
float(Value), !,
rdf_equal(Type, xsd:double),
tw_typed_literal(Type, Value, State, Out).
tw_literal(literal(Value), State, Out) :-
xml_is_dom(Value), !,
rdf_equal(Type, rdf:'XMLLiteral'),
tw_typed_literal(Type, Value, State, Out).
tw_literal(Literal, _State, _Out) :-
type_error(rdf_literal, Literal).
tw_typed_literal(Type, Value, State, Out) :-
tw_abbreviated_literal(Type, Value, State, Out), !.
tw_typed_literal(Type, Value, State, Out) :-
(atom(Value) ; string(Value)), !,
tw_quoted_string(Value, State, Out),
write(Out, '^^'),
tw_resource(Type, State, Out).
tw_typed_literal(Type, Value, State, Out) :-
rdf_equal(Type, rdf:'XMLLiteral'), !,
with_output_to(string(Tmp),
xml_write(Value, [header(false)])),
tw_quoted_string(Tmp, State, Out),
write(Out, '^^'),
tw_resource(Type, State, Out).
tw_typed_literal(Type, Value, State, Out) :-
format(string(Tmp), '~q', [Value]),
tw_quoted_string(Tmp, State, Out),
write(Out, '^^'),
tw_resource(Type, State, Out).
%% tw_abbreviated_literal(+Type, +Value, +State, +Out) is semidet.
%
% Turtle abbreviated typed literals.
%
% @tbd: Deal with canonical forms (or is this a task of the
% RDF parser?
% @tbd: What if the value is not in the lexical space of the type?
term_expansion((tw_abbreviated_literal(NS:Local, Value, State, Out) :- Body),
(tw_abbreviated_literal(Type, Value, State, Out) :- Body)) :-
atom(NS),
rdf_global_id(NS:Local, Type).
tw_abbreviated_literal(xsd:integer, Value, State, Out) :-
( tw_state_canonize_numbers(State, false)
-> write(Out, Value)
; atom_number(Value, Int),
format(Out, '~d', [Int])
).
tw_abbreviated_literal(xsd:double, Value, State, Out) :-
( tw_state_canonize_numbers(State, false)
-> write(Out, Value)
; atom_number(Value, Float),
format(Out, '~f', [Float])
).
tw_abbreviated_literal(xsd:decimal, Value, _, Out) :-
format(Out, '~w', [Value]).
tw_abbreviated_literal(xsd:boolean, Value, _, Out) :-
format(Out, '~w', [Value]).
%% tw_quoted_string(+Atom, +State, +Out) is det.
%
% Write Atom to Out as a quoted string. We only use the
% single-"..." representation.
tw_quoted_string(Atom, _, Out) :-
turtle_write_quoted_string(Out, Atom).
/*******************************
* COMMENT *
*******************************/
comment(State, Format, Args, Out) :-
tw_state_comment(State, true), !,
format(Out, '~n# ', []),
format(Out, Format, Args),
format(Out, '~n', []).
comment(_, _, _, _).
/*******************************
* STATISTICS *
*******************************/
inc_triple_count(State, Count) :-
tw_state_triple_count(State, C0),
C1 is C0+Count,
nb_set_triple_count_of_tw_state(C1, State).
:- multifile
prolog:message//1.
prolog:message(rdf(saved(File, Time, SavedSubjects, SavedTriples))) -->
[ 'Saved ~D triples about ~D subjects into ~p (~3f sec)'-
[SavedTriples, SavedSubjects, File, Time]
].
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