- From: Sandro Hawke <sandro@w3.org>
- Date: Wed, 26 Sep 2012 13:48:43 -0400
- To: Lee Feigenbaum <lee@thefigtrees.net>
- CC: W3C RDF WG <public-rdf-wg@w3.org>
On 09/26/2012 12:50 PM, Lee Feigenbaum wrote: > I'm not sure if this is at all helpful input, but here's how we handle > metadata -- in general -- in Anzo. Pat, you may avert your eyes > because the semantics are inconsistent at best. > :-) Thanks for the details... > A couple of "regular" named graphs > > <p1> { <p1> a ex:Person ; foaf:name "Lee" ... } > <p2> { <p2> a ex:Person ; foaf:name "Lynn" ... } > > Named graphs have corresponding "metadata" graphs > > <mdg1> { <mdg1> a anzo:MetadataGraph . <p1> a anzo:NamedGraph ; > anzo:hasMetadataGraph <mdg1> ; anzo:createdBy ... ; > anzo:lastModifiedBy ... ; anzo:lastModifiedAt ... ; ... } > <mdg2> { <mdg2> a anzo:MetadataGraph . <p2> a anzo:NamedGraph ; > anzo:hasMetadataGraph <mdg2> ; anzo:createdBy ... ; > anzo:lastModifiedBy ... ; anzo:lastModifiedAt ... ; ... } > > We also have first-class datasets, that are represented roughly like: > > <ds1> { <ds1> a anzo:Dataset ; anzo:hasDefaultGraph <p1> ; > anzo:hasNamedGraph <p1>, <p2> } > > Of course, <ds1> is also a regular named graph, so there's a > corresponding metadata graph with metadata about the dataset: > > <mdg3> { <mdg3> a anzo:MetadataGraph . <ds1> a anzo:NamedGraph ; > anzo:hasMetadataGraph <mdg3> ; anzo:createdBy ... ; > anzo:lastModifiedBy ... ; anzo:lastModifiedAt ... ; ... } > > Among other things, we use these datasets directly within SPARQL by > extending SPARQL with a FROM DATASET clause: > > SELECT ... > FROM DATASET <ds1> > WHERE { ... } > > ...which would be equivalent in this example to > > SELECT ... > FROM <p1> > FROM NAMED <p1> > FROM NAMED <p2> > WHERE { ... } > > When we import TriG, we generally are just doing either a replace or > an add on the data in the named graphs in the TriG file. We generally > don't automatically create anzo:Dataset's based on the contents of a > particular TriG file. Instead, if we were exporting and then importing > a dataset, we'd just include the <ds1> graph in our export so we'd > have it back again in an import in the future. > > Regarding your question (a), Sandro, you can always find the metadata > graph for a particular graph (including a dataset graph) simply by > querying for the anzo:hasMetadataGraph triple. > What if I put some anzo:hasMetadataGraph triples in my [other-vendor] SPARQL system, then told Anzo to incorporate that data into my corporate processing system. That could really confuse the system, right? In your commercial environment I guess that's not a big problem -- you can just say "well, don't do that!". Or do you support the idea of from-the-wild data feeds, which are then filtered and queried? What if some of those accidentally or maliciously had hasMetadataGraph triples in them? I suppose you could block those on import, but that wouldn't work for other use cases, where you're trying to exchange datasets with metadata. > Anyway, for what it's worth. > It is nice to be grounded in reality. Plus, Anzo is cool. - s > Lee > > On 9/26/2012 8:53 AM, Sandro Hawke wrote: >> I'm surprised at some of the responses about the metadata questions >> in my "Dataset Syntax - checking for consensus" email [1]. >> >> When people publish RDF for real, don't they usually put some triples >> in it which indicates who created it, when it was created, and maybe >> why? Maybe some folks don't do this, but many people consider this >> an essential practice. My sense is that every computer format >> either has a metadata mechanism built into it, or one somehow gets >> hacked in later (like the javadoc conventions). In a few cases (like >> the Adobe formats) that metadata is expressed in RDF. >> >> When people publish an RDF dataset, aren't they going to want to do >> the same thing? >> >> Yes, sometimes you can just throw that metadata into a named graph, >> but what if (a) you don't get a chance to tell the consumer which >> named graph you put it in, and (b) some named graphs are >> opaque/untrustred, perhaps because they contain old information or >> information from other souces (eg a Web Crawl). (While these might >> not be the cases you work with, it seems to me they'll be quite >> common if this syntax ever catches on.) >> >> Folks who are not convinced we need a metadata mechanism -- how do >> you imagine solving this problem? How can someone reading a >> serialized dataset figure out which triples are the metadata? >> >> -- Sandro >> >> >> >> [1] http://lists.w3.org/Archives/Public/public-rdf-wg/2012Sep/0249.html >> >> > >
Received on Wednesday, 26 September 2012 17:48:57 UTC