- From: Sandro Hawke <sandro@w3.org>
- Date: Tue, 18 Sep 2012 10:40:08 -0400
- To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
- CC: David Wood <david@3roundstones.com>, "public-rdf-wg@w3.org Group WG" <public-rdf-wg@w3.org>
- Message-ID: <505887C8.8000004@w3.org>
On 09/18/2012 09:27 AM, Peter F. Patel-Schneider wrote: > > On 09/18/2012 09:12 AM, Sandro Hawke wrote: >> On 09/18/2012 09:05 AM, Peter F. Patel-Schneider wrote: >>> >>> On 09/17/2012 04:46 PM, Sandro Hawke wrote: >>>> On 09/17/2012 02:02 PM, Peter F. Patel-Schneider wrote: >>>> >>> [...] >>>> >>>> Can you be a little more specific, and tell a story about something >>>> specific someone is likely to want to do that they could do with >>>> your proposed semantics and not with the proposal on the agenda? >>>> >>>> (The two things I see are: (1) the default graph being "asserted", >>>> which seems easy enough to work around if desired [just use a named >>>> graph], and (2) URIs being interpreted the same way throughout the >>>> dataset... but I can't see what harm that could cause. Maybe I'm >>>> on the wrong track. Okay, I'm also concerned about >>>> unwanted-but-valid inference being done, but that's an issue >>>> throughout RDF, not just about datasets.) >>>> >>>> -- Sandro >>>> >>> >>> (2) I don't know where in the minimal semantics there is a notion >>> that IRIs have to be interpreted the same way throughout the >>> dataset, so I don't see any difference here. If, however, there is a >>> need to interpret IRIs the same way throughout a dataset then this >>> would indeed be a vast difference, essentially requiring rigid >>> designators in datasets. This would mean that any equality >>> assertion in the default graph would carry over into the named >>> graphs (and maybe vice versa). >>> >> >> Sorry, I just meant the IRIs of the named graphs, the n's in the >> <n,g> pairs, being interpreted the same as IRIs the default graph. > > OK, so you are referring to the part of the semantics where it is the > denotation of the graph names in the default graph that is used as the > start of the mapping to the named graph itself. I am against this > because there can be strange bleeding from the default graph to the > identity of the named graphs, such as in example 2.16 in > http://www.w3.org/2011/rdf-wg/wiki/TF-Graphs/Minimal-dataset-semantics > although the analysis there is incorrect. > > if all you are dong is recording named graphs, then why should > information in the default graph potentially cause two named graphs to > be smushed together? > How could it not? If I know <g1> { ... } <g2> { ... } and if I know, because of some metadata, that g1 and g2 are actually the same thing, doesn't that imply some kind of smushing or inconsistency? >>> (1) Even if you used an empty default graph, you get some carry-over >>> into the named graphs. For example, the named graph resources can >>> only be taken from the resources in this interpretation. Fortunately >>> (or unfortunately) all RDF interpretations are infinite, so there >>> probably are no observable consequences. >>> >>> But in any case, why should I be forced into turning my default >>> graph into a named graph (with some arbitrary name) and adding an >>> empty default graph? >>> >>> >>> One interesting use of RDF datasets is to collect information from >>> the web. The named graphs record the source of the graphs and >>> their contents. The default graph can either be related to these >>> collected graphs or unrelated to them. Having the default graph >>> affect the meaning of the named graphs is undesired. >>> >> >> I don't see how you can usefully communicate collected information >> like that unless you have a private protocol arranged (in which case >> this is all moot), or you use the default graph for metadata. >> >> -- Sandro >> > > I would turn this question around and ask how the current minimal > semantics can be used for the same purpose. > I'm not sure I can answer that. The one thing I can argue for, I think, is that the graph names be strongly connected to those same names being used in the default graph. For example, I think we need to be able to say things like this: <http://example.org/d1> { <a> <b> 1 }. <http://example.org/d1> eg1:lastModified "Wed, 12 Sep 2012 11:42:31 GMT". where eg1:lastModified is defined such that this dataset conveys the knowledge that (1) a dereference on URL "http://example.org/d1" was done; (2) it resulted in (at least?) the triple { <a> <b> 1 }; and (3) the HTTP Last-Modified header returned during that dereference was the string "Wed, 12 Sep 2012 11:42:31 GMT". (I'm not suggesting this group standardize eg1:lastModified, or that this is a good way to convey this information; I'm just saying that I think someone, someday needs to be able to define vocabularies like this, given the work we are doing now. That seems to me to be our key graph-semantics deliverable.) > I also don't see why excluding useful private ways of doing things > (particularly ones that might already be in use) is moot. > Well, I think these standards only apply between systems, not within systems. Private communications are essentially system-internals, and none of our business. Right? > I didn't exclude using the default graph to record information about > the named graphs and their sources. However, I didn't want > information in the default graph to affect the situation in the named > graphs. > My concern/motivation is in my example above. The semantics need to be strong enough that eg1:lastModified can be defined to make my example dataset mean to consumers what the producer wants it to mean. I leave any argument for more powerful semantics to others, who have other use cases in mind. -- Sandro > peter > >
Received on Tuesday, 18 September 2012 14:40:25 UTC