Hi, > Yes, I encountered the same problem recently. The problem is the same > when using Special:ExportRDF and possibly also when trying to use a > SPARQL store (though I am not sure about this). It occurs whenever PageB > redirects to PageA, and PageA has subobjects (including #ask queries).
Thanks Markus, with above information I was able to reproduce the issue which is now tracked under [0]. [0] https://github.com/SemanticMediaWiki/SemanticMediaWiki/issues/619 Cheers On 11/11/14, Markus Krötzsch <mar...@semantic-mediawiki.org> wrote: > Hi Daniel, > > On 10.11.2014 20:31, Herzig, Daniel (AIFB) wrote: >> >> Problem #1: export of RDF fails with "Data for a subobject of PageA >> cannot be added to PageB'" > > Yes, I encountered the same problem recently. The problem is the same > when using Special:ExportRDF and possibly also when trying to use a > SPARQL store (though I am not sure about this). It occurs whenever PageB > redirects to PageA, and PageA has subobjects (including #ask queries). > > The problem is based on SMW's handling of redirects. In query answering > etc., SMW will follow redirects, i.e., when you use a redirect page in > any request or query, you will get the answer as if you would have used > the redirect target instead. There are some places where this can be > switched off, but especially the SMWStore method getSemanticData() does > not support this. This means that any attempt to get the semantic data > (the stuff shown in the Factbox) for a redirect page will return the > data for the redirect target. > > You can see this effect when using Special:Browse on a redirect page. > Notably, however, this does not cause any exception. Something else must > be going wrong in the RDF export. My guess is that the call to > getSubSemanticData() in SMW_ExportController.php(128) does in general > cause an exception for SemanticData objects that have been created from > redirects. Special:Browse would not run into this because the data for > the subobjects is not expanded there (you only get links to show the > subobject-data, but these links will trigger new requests that are not > based on redirects). > > The exception itself happens since a subobject of PageA is added to the > data for PageB. This should not happen. In the situation with the > redirect, the semantic data returned would need to use the redirect > target as a subject if it wants to have the subobjects. This should be > modified in the SQL store method. I am pretty confident that this will > fix the exception. > > This fix is not a complete solution for RDF, since it will mean that > every redirect page exports the exact same data of its target page. So > the dump will contain duplicate triples, and it will lack any > information about redirects (they will not even be mentioned). A better > handling would be to recognize that we are dealing with a redirect page, > and to export it as such (in particular, do not call getSemanticData()). > The right place to do this would be the method getSemanticData() in > SMW_ExportController.php(294). It could check if a page is a redirect > and then create a suitable SemanticData response manually for this case. > > Another option would be to extend the store to support redirect > resolution to be turned off for getSemanticData() by using some > parameter. Care is needed there to make sure that the caching is not > confused (but this seems easier if the subject is correctly converted to > be the redirect target; so requests with and without redirect resolution > will eventually use distinct subjects, and these should be the basis for > caching). > > Cheers, > > Markus > > > >> ---------------------------------------------------------- >> When running SemanticMediaWiki/maintenance/dumpRDF.php following >> exception occurs, stack below [2]: 'Data for a subobject of PageA cannot >> be added to PageB' >> >> PageB is a redirect to PageA. PageB used lots of template with semantic >> data. When the information on PageB became outdated, a redirect has been >> inserted to point the newer page PageA. PageA uses also lots of >> templates with subobjects. >> >> Deleting page PageB solves the issue. However, there are thousands of >> redirects in this wiki and they can't be deleted. >> Unfortunately, I can not reproduce this issue in my test environment >> (same SMW and MW versions) and I have no developer access to the system >> having this problem. >> >> Did anybody encountered this issue too? Any ideas how to fix this? >> >> My assumption was that the reason for this bug lies in inconsistent >> semantic data. Maybe because some refreshJobs aren't done yet. >> When trying to debug redirects and data refresh jobs in my test >> environment, I encountered the problem with job loops and redirects, >> which might be connected: >> >> >> Problem #2: Infinite jobqueue runs >> ---------------------------------------------------------- >> There was a discussion on infinite jobqueue runs recently on this list. >> However, I found this way easier to reproduce the problem. >> When inserting a redirect into a page that existed before and had >> semantic data on it, two SMW_UpdateJobs are inserted into the queue. >> When executed, these jobs spawn identical jobs, which causes the queue >> to loop forever. >> I can reproduce this behavior with the following procedure: >> >> * Create a page and insert a subobject. Save the page. >> * Edit the page again and insert a redirect, i.e. #REDIRECT >> [[AnotherPage]]. Save the page. >> ** The table 'smw_fpt_redi' has no entry for this page. I think there >> should be one, right? >> ** The subobject and its properties are still in table 'smw_object_ids' >> and the page is not marked as redirect. >> ** Now two new SMW_UpdateJobs are in the queue (one for origin page, one >> for target page of the redirect). When executed, these jobs spawn >> identical jobs again -> loops forever >> ** The RDF dump still produces the page with its subobject. >> >> truncate smw_object_ids, smw_prop_stats; and runnning rebuildData.php >> shows the page as a redirect in smw_object_ids. Just running >> rebuildData.php alone does not help. >> >> I assume the solution would be to detect that a redirect has been >> inserted into a page that has semantic data and removed its semantic >> data properly. >> Unfortunately, I haven't found a way to do this. >> >> Any hints and suggestions are appreciated! >> >> >> >> Thanks! >> Daniel >> >> >> >> >> [1] >> MediaWiki 1.22.7 >> Semantic MediaWiki 2.0 >> >> >> [2] >> >> Exception from line 601 of >> www/htdocs/extensions/SemanticMediaWiki/includes/SemanticData.php: Data >> for a subobject of PageA cannot be added to PageB. >> Backtrace: >> #0 >> www/htdocs/extensions/SemanticMediaWiki/includes/storage/SQLStore/SMW_Sql3StubSemanticData.php(320): >> SMW\SemanticData->addSubSemanticData(SMWSql3StubSemanticData) >> #1 >> www/htdocs/extensions/SemanticMediaWiki/includes/storage/SQLStore/SMW_Sql3StubSemanticData.php(171): >> SMWSql3StubSemanticData->addSubSemanticDataToInternalCache(SMW\DIProperty) >> #2 >> www/htdocs/extensions/SemanticMediaWiki/includes/export/SMW_ExportController.php(128): >> SMWSql3StubSemanticData->getSubSemanticData() >> #3 >> www/htdocs/extensions/SemanticMediaWiki/includes/export/SMW_ExportController.php(452): >> SMWExportController->serializePage(SMW\DIWikiPage, integer) >> #4 >> www/htdocs/extensions/SemanticMediaWiki/includes/export/SMW_ExportController.php(422): >> SMWExportController->printAll(boolean, integer, integer) >> #5 www/htdocs/extensions/SemanticMediaWiki/maintenance/dumpRDF.php(158): >> SMWExportController->printAllToOutput(boolean, integer, integer) >> #6 www/htdocs/extensions/SemanticMediaWiki/maintenance/dumpRDF.php(92): >> SMW\Maintenance\DumpRdf->generateRdfToChannel() >> #7 www/htdocs/maintenance/doMaintenance.php(113): >> SMW\Maintenance\DumpRdf->execute() >> #8 www/htdocs/extensions/SemanticMediaWiki/maintenance/dumpRDF.php(164): >> require_once(string) >> #9 {main} >> >> >> >> ------------------------------------------------------------------------------ >> Comprehensive Server Monitoring with Site24x7. >> Monitor 10 servers for $9/Month. >> Get alerted through email, SMS, voice calls or mobile push notifications. >> Take corrective actions from your mobile device. >> http://pubads.g.doubleclick.net/gampad/clk?id=154624111&iu=/4140/ostg.clktrk >> >> >> >> _______________________________________________ >> Semediawiki-devel mailing list >> Semediawiki-devel@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/semediawiki-devel >> > > > ------------------------------------------------------------------------------ > Comprehensive Server Monitoring with Site24x7. > Monitor 10 servers for $9/Month. > Get alerted through email, SMS, voice calls or mobile push notifications. > Take corrective actions from your mobile device. > http://pubads.g.doubleclick.net/gampad/clk?id=154624111&iu=/4140/ostg.clktrk > _______________________________________________ > Semediawiki-devel mailing list > Semediawiki-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/semediawiki-devel > ------------------------------------------------------------------------------ Comprehensive Server Monitoring with Site24x7. Monitor 10 servers for $9/Month. Get alerted through email, SMS, voice calls or mobile push notifications. Take corrective actions from your mobile device. http://pubads.g.doubleclick.net/gampad/clk?id=154624111&iu=/4140/ostg.clktrk _______________________________________________ Semediawiki-devel mailing list Semediawiki-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/semediawiki-devel
