1/* $Id$ 2 3 Part of SWI-Prolog 4 5 Author: Jan Wielemaker 6 E-mail: wielemak@science.uva.nl 7 WWW: http://www.swi-prolog.org 8 Copyright (C): 1985-2007, University of Amsterdam 9 10 This program is free software; you can redistribute it and/or 11 modify it under the terms of the GNU General Public License 12 as published by the Free Software Foundation; either version 2 13 of the License, or (at your option) any later version. 14 15 This program is distributed in the hope that it will be useful, 16 but WITHOUT ANY WARRANTY; without even the implied warranty of 17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 18 GNU General Public License for more details. 19 20 You should have received a copy of the GNU General Public 21 License along with this library; if not, write to the Free Software 22 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 23 24 As a special exception, if you link this library with other files, 25 compiled with a Free Software compiler, to produce an executable, this 26 library does not by itself cause the resulting executable to be covered 27 by the GNU General Public License. This exception does not however 28 invalidate any other reasons why the executable file might be covered by 29 the GNU General Public License. 30*/ 31 32:- module(rdf_history, 33 [ rdfh_transaction/1, % :Goal 34 rdfh_assert/3, % +S,+P,+O 35 rdfh_retractall/3, % +S,+P,+O 36 rdfh_update/3, % +S[->NS],+P[->NP],+O[->[NO] 37 rdfh_db_transaction/3, % ?DB, +Condition, ?Transaction 38 rdfh_triple_transaction/2, % +Triple, -Transaction 39 rdfh_transaction_member/2 % ?Action, +Transaction 40 ]). 41:- use_module(library('http/http_session')). 42:- use_module(library(lists)). 43:- use_module(library(record)). 44:- use_module(library(error)). 45:- use_module(library(debug)). 46:- use_module(library('semweb/rdf_persistency')). 47:- use_module(library('semweb/rdf_db')).
72 /******************************* 73 * DECLARATIONS * 74 *******************************/ 75 76:- module_transparent 77 rdfh_transaction/1. 78 79:- rdf_meta 80 rdfh_assert(r,r,o), 81 rdfh_retractall(r,r,o), 82 rdfh_update(t,t,t). 83 84:- multifile 85 rdfh_hook/1. 86 87:- record 88 rdf_transaction(id:integer, 89 nesting:integer, 90 time:number, 91 message, 92 actions:list, 93 other_graphs:list). 94 95 96 /******************************* 97 * MODIFICATIONS * 98 *******************************/
105rdfh_transaction(Goal) :-
106 rdfh_user(User),
107 transaction_context(Context),
108 rdf_transaction(, log(rdfh([user(User)|Context]), User)).
116rdfh_assert(S,P,O) :-
117 ( rdf_active_transaction(log(rdfh(_), User))
118 -> rdfh_time(Time),
119 rdf_assert(S,P,O,User:Time)
120 ; throw(error(permission_error(assert, triple, rdf(S,P,O)),
121 context(_, 'No rdfh_transaction/1')))
122 ).One of the problems we are faced with is that a retract action goes into the journal of the user whose triple is retracted, which may or may not be the one who performed the action.
136rdfh_retractall(S,P,O) :-
137 ( rdf_active_transaction(log(rdfh(_), _User))
138 -> rdf_retractall(S,P,O)
139 ; throw(error(permission_error(retract, triple, rdf(S,P,O)),
140 context(_, 'No rdfh_transaction/1')))
141 ).
Current simple-minded approach is to turn an update into a
retract and assert. The S,P,O specifications are either a ground
value or of the form Old -> New. Here is an example:
rdfh_update(Work, Style, wn:oldstyle -> wn:newstyle)
160rdfh_update(S,P,O) :- 161 ( rdf_active_transaction(log(rdfh(_), User)) 162 -> update(S,P,O, rdf(RS, RP, RO), rdf(AS, AP, AO)), 163 must_be(ground, RS), 164 must_be(ground, RP), 165 must_be(ground, RO), 166 rdfh_time(Time), 167 rdf_retractall(RS, RP, RO), 168 rdf_assert(AS, AP, AO, User:Time) 169 ; throw(error(permission_error(retract, triple, rdf(S,P,O)), 170 context(_, 'No rdfh_transaction/1'))) 171 ). 172 173update(Ss, Ps, Os, rdf(S0, P0, O0), rdf(S,P,O)) :- 174 update(Ss, S0, S), 175 update(Ps, P0, P), 176 update(Os, O0, O). 177 178update(From->To, From, To) :- !. 179update(Value, Value, Value).
188transaction_context(Context) :-
189 ( rdfh_session(Session)
190 -> Context = [session(Session)]
191 ; Context = []
192 ).198rdfh_session(Session) :- 199 rdfh_hook(session(Session)), !. 200rdfh_session(Session) :- 201 catch(http_session_id(Session), _, fail).
210rdfh_user(User) :- 211 rdfh_hook(user(User)), !. 212rdfh_user(OpenId) :- 213 http_session_data(openid(OpenId)).
220rdfh_time(Seconds) :- 221 get_time(Now), 222 Seconds is round(Now). 223 224 225 /******************************* 226 * EXAMINE HISTORY * 227 *******************************/
233rdfh_triple_transaction(rdf(S,P,O), Transaction) :-
234 rdf(S,P,O,DB:Time),
235 After is Time - 1,
236 rdfh_db_transaction(DB, after(After), Transaction),
237 rdfh_transaction_member(assert(S,P,O,Time), Transaction).255rdfh_db_transaction(DB, true, Transaction) :- !, 256 rdf_journal_file(DB, Journal), 257 journal_transaction(Journal, Transaction). 258rdfh_db_transaction(DB, id(Id), Transaction) :- !, 259 must_be(atom, DB), 260 rdf_journal_file(DB, Journal), 261 open_journal(Journal, Fd), 262 call_cleanup((seek_journal(Fd, id(Id)), 263 read_transaction(Fd, Transaction)), 264 close(Fd)). 265rdfh_db_transaction(DB, Condition, Transaction) :- !, 266 valid_condition(Condition), 267 rdf_journal_file(DB, Journal), 268 open_journal(Journal, Fd), 269 seek_journal(Fd, Condition), 270 stream_transaction(Fd, Transaction). 271 272valid_condition(Var) :- 273 var(Var), !, 274 instantiation_error(Var). 275valid_condition(after(Time)) :- !, 276 must_be(number, Time). 277valid_condition(Cond) :- 278 type_error(condition, Cond).
284open_journal(JournalFile, Fd) :-
285 open(JournalFile, read, Fd, [encoding(utf8)]).291journal_transaction(JournalFile, Transaction) :- 292 open_journal(JournalFile, Fd), 293 stream_transaction(Fd, Transaction). 294 295stream_transaction(JFD, Transaction) :- 296 call_cleanup(read_transaction(JFD, Transaction), close(JFD)). 297 298read_transaction(In, Transaction) :- 299 repeat, 300 read(In, T0), 301 ( T0 == end_of_file 302 -> !, fail 303 ; transaction(T0, In, T), % transaction/3 is not steadfast 304 T = Transaction 305 ). 306 307transaction(begin(Id, Nest, Time, Msg), In, 308 rdf_transaction(Id, Nest, Time, Msg, Actions, Others)) :- !, 309 read(In, T2), 310 read_transaction_actions(T2, Id, In, Actions, Others). 311transaction(start(_), _, _) :- !, fail. % Open journal 312transaction(end(_), _, _) :- !, fail. % Close journal 313transaction(Action, _, Action). % Action outside transaction? 314 315read_transaction_actions(end(Id, _, Others), Id, _, [], Others) :- !. 316read_transaction_actions(end_of_file, _, _, [], []) :- !. % TBD: Incomplete transaction (error) 317read_transaction_actions(Action, Id, In, Actions, Others) :- 318 ignore_in_transaction(Action), !, 319 read(In, T2), 320 read_transaction_actions(T2, Id, In, Actions, Others). 321read_transaction_actions(Action, Id, In, [Action|Actions], Others) :- 322 read(In, T2), 323 read_transaction_actions(T2, Id, In, Actions, Others). 324 325ignore_in_transaction(start(_)). 326ignore_in_transaction(end(_)). 327ignore_in_transaction(begin(_,_,_,_)). 328ignore_in_transaction(end(_,_,_)).
The implementation relies on the incrementing identifier numbers and time-stamps.
346seek_journal(Fd, Spec) :- 347 stream_property(Fd, file_name(File)), 348 size_file(File, Size), 349 Here is Size//2, 350 Last = last(-), 351 ( is_after_spec(Spec) 352 -> ( bsearch_journal(Fd, 0, Here, Size, Spec, Last) 353 -> true 354 ; arg(1, Last, StartOfTerm), 355 StartOfTerm \== (-), 356 seek(Fd, StartOfTerm, bof, _) 357 ) 358 ; bsearch_journal(Fd, 0, Here, Size, Spec, Last) 359 ). 360 361is_after_spec(after(_Time)).
367bsearch_journal(Fd, Start, Here, End, Spec, Last) :- 368 start_of_transaction(Fd, Here, StartOfTerm, Begin), !, 369 compare_transaction(Spec, Begin, Diff), 370 ( Diff == (=) 371 -> seek(Fd, StartOfTerm, bof, _) 372 ; Diff == (<) 373 -> NewHere is Start+(Here-Start)//2, 374 NewHere < Here, 375 nb_setarg(1, Last, StartOfTerm), 376 bsearch_journal(Fd, Start, NewHere, Here, Spec, Last) 377 ; NewHere is StartOfTerm+(End-StartOfTerm)//2, 378 NewHere > StartOfTerm, 379 bsearch_journal(Fd, StartOfTerm, NewHere, End, Spec, Last) 380 ). 381bsearch_journal(Fd, Start, Here, _End, Spec, Last) :- 382 NewHere is Start+(Here-Start)//2, 383 NewHere < Here, 384 bsearch_journal(Fd, Start, NewHere, Here, Spec, Last). 385 386compare_transaction(id(Id), begin(Id2,_,_,_), Diff) :- !, 387 compare(Diff, Id, Id2). 388compare_transaction(after(Time), begin(_,_,T,_), Diff) :- !, 389 compare(Diff, Time, T).
396start_of_transaction(Fd, From, Start, Term) :- 397 seek(Fd, From, bof, _), 398 skip(Fd, 10), 399 repeat, 400 seek(Fd, 0, current, Start), 401 read(Fd, Term), 402 ( transaction_start(Term) 403 -> ! 404 ; Term == end_of_file 405 -> !, fail 406 ; fail 407 ). 408 409transaction_start(begin(_Id,_Nest,_Time,_Message)).
415rdfh_transaction_member(Action, Transaction) :-
416 rdf_transaction_actions(Transaction, Actions),
417 member(Action, Actions)
RDF Persistent store change history
This module deals with accessing the journal files of the RDF persistency layer to get insight in the provenance and history of the RDF database. It is designed for Wiki-like collaborative editing of an RDF graph. We make the following assumptions: