Thanks for the feedback, just a note to say that I responded via https://www.wikidata.org/wiki/Wikidata:Contact_the_development_team/Query_Service_and_search
David Causse On Thu, Apr 16, 2020 at 8:16 PM Peter F. Patel-Schneider < pfpschnei...@gmail.com> wrote: > I am taking the liberty of replying to the list because of the problems > with > supplied justification for this change that are part of the original > message. > > I believe that https://phabricator.wikimedia.org/T244341#5889997 is > inadequate > for determining that blank nodes are problematic. First, the fact that > determining isomorphism in RDF graphs with blank nodes is non-polynomial > is a > red herring. If the blank nodes participate in only one triple then > isomorphism remains easy. Second, the query given to remove a some-value > SNAK > is incorrect in general - it will remove all triples with the blank node as > object. (Yes, if the blank nodes found are leaves then no extra triples > are > removed.) A simpler DELETE WHERE will have the seemingly-desired result. > > This is not to say that blank nodes do not cause problems. According to > the > semanticss of both RDF and SPARQL blank nodes are anonymous so to > repeatedly > access the same blank node in a graph one has to access the stored graph > using > an interface that exposes the retained identity of blank nodes. It looks > as > if the WDSQ is built on a system that has such an interface. As the WDQS > already uses user-visible features that are not part of SPARQL, adding (or > maybe even only utilizing) a non-standard interface that is only used > internally would not be a problem. > > One problem when using generated URLs to replace blank nodes is that these > generated URLs have to be guaranteed stable and unique (not just stable) > for > the lifetime of the query service. Another problem is that yet another > non-standard function is being introduced, pulling the RDF dump of Wikidata > yet further from RDF. > > So this is a significant change as far as users are concerned that also has > potential implementation issues. Why not just use an internal interface > that > exposes a retained identity for blank nodes? > > Peter F. Patel-Schneider > > > > On 4/16/20 8:34 AM, David Causse wrote: > > Hi, > > > > This message is relevant for people writing SPARQL queries and using the > > Wikidata Query Service: > > > > As part of the work of redesigning the WDQS updater[0] we identified that > > blank nodes[1] are problematic[2] and we plan to deprecate their usage in > > the wikibase RDF model[3]. To ease the deprecation process we are > > introducing the new function wikibase:isSomeValue() that can be used in > > place of isBlank() when it was used to filter SomeValue[4]. > > > > What does this mean for you: nothing will change for now, we are only > > interested to know if you encounter any issues with the > > wikibase:isSomeValue() function when used as a replacement of the > isBlank() > > function. More importantly, if you used the isBlank() function for other > > purposes than identifying SomeValue (unknown values in the UI), please > let > > us know as soon as possible. > > > > The current plan is as follow: > > > > 1. Introduce a new wikibase:isSomeValue() function > > We are at this step. You can already use wikibase:isSomeValue() in the > Query > > Service. Here’s an example query (Humans whose gender we know we don't > know): > > SELECT ?human WHERE { > > ?human wdt:P21 ?gender > > FILTER wikibase:isSomeValue(?gender) . > > } > > You can also search the wikis[8] to find all the pages where the function > > isBlank is referenced in a SPARQL query. > > > > 2. Generate stable labels for blank nodes in the wikibase RDF output > > Instead of "autogenerated" blank node labels wikidata will now provide a > > stable label for blank nodes. In other words the wikibase triples using > > blank nodes such as: > > s:Q2-6657d0b5-4aa4-b465-12ed-d1b8a04ef658 ps:P576 _:genid2 ; > > will become > > s:Q2-6657d0b5-4aa4-b465-12ed-d1b8a04ef658 ps:P576 > > _:1668ace9a6860f7b32569c45fe5a5c0d ; > > This is not a breaking change. > > > > 3. [BREAKING CHANGE] Convert blank nodes to IRIs in the WDQS updater > > At this point some WDQS servers will start returning IRIs such > > as http://www.wikidata.org/somevalue/1668ace9a6860f7b32569c45fe5a5c0d > (the > > exact form of the IRI is still under discussion) instead of blank node > > literals like t1514691780 auto-generated by blazegraph. Queries still > using > > isBlank() will stop functioning. Tools explicitly relying on the > presence of > > blank nodes (t1514691780) in the query results will also be affected. > > We don’t have a defined date for this change yet, but we will follow the > > Wikidata breaking change process (announcing the change 4 weeks in > advance). > > > > 4. [BREAKING CHANGE] Change the RDF model and remove blank nodes > completely > > from the RDF dumps > > Instead of doing the conversion and blank node removal in the WDQS > updater > > we will do it at RDF generation. > > This is a breaking change of the somevalue section of the RDF model[5] > and > > the no value owl constraint for properties[6]. > > We don’t have a defined date for this change yet, but we will follow the > > Wikidata breaking change process (announcing the change 4 weeks in > advance). > > > > If you encounter issues using wikibase:isSomeValue() or if you have > > questions about the process, feel free to write a comment on the > Phabricator > > ticket[3] or the Contact the development team (query service and search) > > wiki page[7]. > > > > Thanks! > > > > -- > > David Causse > > > > 0: https://phabricator.wikimedia.org/T244590 > > 1: https://en.wikipedia.org/wiki/Blank_node > > 2: https://phabricator.wikimedia.org/T244341#5889997 > > 3: https://phabricator.wikimedia.org/T244341 > > 4: > https://www.mediawiki.org/wiki/Wikibase/DataModel#PropertySomeValueSnak > > 5: > https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format#Somevalue > > 6: > https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format#Novalue > > 7: > https://www.wikidata.org/wiki/Wikidata:Contact_the_development_team/Query_Service_and_search > > 8: > https://www.wikidata.org/w/index.php?search=all%3Ainsource%3A%2FisBlank+%2A%5C%28+%2A%5C%3F%2Fi&title=Special:Search&profile=default&fulltext=1 > > > > > > > > _______________________________________________ > > Wikidata-tech mailing list > > Wikidata-tech@lists.wikimedia.org > > https://lists.wikimedia.org/mailman/listinfo/wikidata-tech > > _______________________________________________ > Wikidata-tech mailing list > Wikidata-tech@lists.wikimedia.org > https://lists.wikimedia.org/mailman/listinfo/wikidata-tech >
_______________________________________________ Wikidata-tech mailing list Wikidata-tech@lists.wikimedia.org https://lists.wikimedia.org/mailman/listinfo/wikidata-tech
