- From: Rob Atkinson <rob@metalinkage.com.au>
- Date: Fri, 02 Sep 2016 22:04:59 +0000
- To: janowicz@ucsb.edu, Frans Knibbe <frans.knibbe@geodan.nl>
- Cc: Joshua Lieberman <jlieberman@tumblingwalls.com>, Jeremy Tandy <jeremy.tandy@gmail.com>, SDW WG Public List <public-sdw-wg@w3.org>
- Message-ID: <CACfF9Lz5CmgRV09LoF9naqOvbixfbkSuLihq+ry6YpaTEwLdzQ@mail.gmail.com>
A few things - this is a rich discussion and we have identified several parts (which is probably why the original issue was hard to pin down) I'm glad we have coaxed one elephant out - the sameAs semantics issue. For me this is the litmus test whether a URL can be used as a URI for a thing or not. (and this is where one of the issues about SIRF Jeremy raised comes in - but I dont think we need to worry about specific approach, rather the criteria for whether a URI is a good one for identification purposes. I think we simply make a strong statement that you dont use a URL as a URI if it is not stable and it does not make sense to use owl:sameAs. This pretty much rules out any direct URL to a single representation: consider two resources with URIs R1 and R2 R1 ns:dateEdited 12/1/2001 R2 ns:dateEdited 6/6/2006 R1 owl:sameAs R2 then leads to ambiguity regarding the value of the functional property ns:dateEdited however U1 --303--> R1 U2 --303--> R2 can (and should be) represented as U1 ns:hasRepresentation R1 U2 ns:hasRepresentation R2 U1 owl:sameAS U2 entails U1 ns:hasRepresentation R1, R2 which doesnt make any stupid statements about the properties. It also allows us to make useful metadata statements about R1, R2 as required. Whilst this is a general concern, we see issues of identification stability, multiple representations, non-unique naming being significant to spatial data and I think we can and should therefore extend the general DWBP with an example using spatial representations and provide a more concrete best practice. On Sat, 3 Sep 2016 at 00:40 Krzysztof Janowicz <janowicz@ucsb.edu> wrote: > I am no expert on the matter, but several sources tell me that if <A> > <owl:sameAs> <B>, then all statements that can be made about A will also be > true for B, and vice versa. It seems that the lighthouse example breaks at > that point. For example, in Jeremy's example one of the lighthouse > representations has a height of 41 m. It is likely that that statement will > be false for the representation of the lighthouse as a ruin. > > Can we be sure that if we recommend using owl:sameAs to assert that two > resources are really the same thing, everyone and everything is aware of > the logical consequences? > > > This is exactly the key point. If A owl:sameAs B than A and B signify the > same entity and thus every *statement* about A is a statement about B. It > works well with Jeremy's example. The fact that the ruin no longer is 41m > tall is an example of the need for spatiotemporal scoping of predicates not > a shortcoming of owl:sameAs. Also, keep in mind that RDF statements have > nothing to do with facts or truth; they are just sets of statements. This > is were the power of RDF comes from. > > Best, > Krzysztof > > > > > On 09/02/2016 02:20 AM, Frans Knibbe wrote: > > > On 1 September 2016 at 23:42, Krzysztof Janowicz <janowicz@ucsb.edu> > wrote: > >> >> Hi, >> >> So as representations, these are not “owl:sameAs”. >> >> >> >> Just for clarification. owl:sameAs is only concerned with the mapping of >> IRIs to (real world) entities and not 'representations' (leaving aside the >> fact that everything is a representation in some sense). I.e., it is about >> 'identity'. To give an extreme example, a URI may refer to the Eddystone >> Lighthouse which may be classified as /Lighthouse/ in some repository. >> Another URI established 50 years from now can still refer to this >> particular (4th) lighthouse and classify it as a /Ruin/. Another 50 years >> into the future, there may be yet another URI that refers to the fact that >> at some stage there was a ruin here of the 4th lighthouse called Eddystone >> while there is nothing physical left of it, and, thus, it is neither >> classified as /Ruin/ nor /Lighthouse/. In fact, we do not even need to >> introduce the concept of "real world" here as we can also establish a >> sameAs relation between two URIs that point to Zeus. Please note that this >> is different from establish a sameAs link between a particular statue of >> Zeus in a particular museum and Zeus as the god of thunder. Finally, the >> purpose of establishing sameAs links is typically data fusion/conflation >> (no matter whether this is done ad-hoc, manually, or (offline) >> computationally) . >> > > I am no expert on the matter, but several sources tell me that if <A> > <owl:sameAs> <B>, then all statements that can be made about A will also be > true for B, and vice versa. It seems that the lighthouse example breaks at > that point. For example, in Jeremy's example one of the lighthouse > representations has a height of 41 m. It is likely that that statement will > be false for the representation of the lighthouse as a ruin. > > Can we be sure that if we recommend using owl:sameAs to assert that two > resources are really the same thing, everyone and everything is aware of > the logical consequences? > > Regards, > Frans > > > >> >> Best, >> Jano >> >> >> On 08/31/2016 06:38 AM, Joshua Lieberman wrote: >> >> Jeremy, >> >> So as representations, these are not “owl:sameAs”. We assume that as >> feature data, each refers to a real world entity, but we don’t assert that >> this VerticalObstruction is the same individual as this >> MaritimeNavigationAid. We just are suspecting or asserting that the same >> real world thing is being discerned in two different ways. Someone may >> define a lighthouse class as subclassing both, otherwise a slightly >> specialized relation (e.g. sdwgeo:sameRealWorldEntityAs) would be useful >> here. >> >> Josh >> >> On Aug 31, 2016, at 8:41 AM, Jeremy Tandy <jeremy.tandy@gmail.com> wrote: >> >> > That still leaves a gap in expressing whether two feature data >> entities represent the same real world entity. Perhaps we need a >> "sameFeatureAs" predicate to address this. >> >> @josh - can we clarify my understanding please? >> >> In the BP doc §4 "Spatial things, features and geometry" [1] I use a >> lighthouse example, so I'll continue with that ... >> >> We have one real lighthouse (Eddystone Lighthouse) that is discerned as a >> different Type by different communities: "VerticalObstruction" and >> "MaritimeNavigationAid". In ISO 19100 parlance, these are two distinct >> feature types. The two "Features" might be encoded in GML as follows >> (forgive any errors in my illustrative example): >> >> <VerticalObstruction gml:id="a"> >> <gml:name>Eddystone</gml:name> >> <gml:identifier codeSpace=" >> http://example.com/sar/features/vo/">EDY</gml:identifier> >> <geometry> >> <gml:Point gml:id="a-p1" srsDimension="2" srsName="EPSG:4326"> >> <gml:pos>50.184 -4.268</gml:pos> >> </gml:Point> >> </geometry> >> <height uom="m">41</height> >> </VerticalObstruction> >> >> <MaritimeNavigationAid gml:id="b"> >> <gml:name>Eddystone Lighthouse</gml:name> >> <gml:identifier codeSpace="http://example.org/maritime/navaid/ >> ">2650253</gml:identifier> >> <geo> >> <gml:Point gml:id="b-p1" srsDimension="2" srsName="EPSG:4326"> >> <gml:pos>50.2 -4.3</gml:pos> >> </gml:Point> >> </geo> >> <lightCharacteristic> >> ... >> </lightCharacteristic> >> </MaritimeNavigationAid> >> >> So we have two Features (which we collectively have agreed are "spatial >> things"), with identifiers <http://example.com/sar/features/vo/EDY> and < >> http://example.org/maritime/navaid/2650253>. Respectively, the XML >> elements that describe these features are identified as "a" and "b" using >> the @gml:id attribute. >> >> If we are using "indirect identification" then _both_ < >> http://example.com/sar/features/vo/EDY> and < >> http://example.org/maritime/navaid/2650253> are treated as identifiers >> for the _real_ Eddystone Lighthouse; we simply don't care to differentiate >> between the real world thing and the information record. In which case, >> <owl:sameAs> would seem sufficient? The "height" and "lightCharacteristic" >> properties are both applicable to the real Eddystone Lighthouse. Some >> judgement would be required to decide which point geometry ("geo" or >> "geometry" property) is considered "best". >> >> The way I think about it, @gml:id is more like the identifier for a named >> graph; a container for a set of properties ... >> >> Am I missing something??? >> >> Jeremy >> >> >> [1]: http://w3c.github.io/sdw/bp/#spatial-things-features-and-geometry >> >> On Wed, 31 Aug 2016 at 12:42 Joshua Lieberman < >> jlieberman@tumblingwalls.com> wrote: >> >>> If we are asserting that spatial data on the Web is "always" feature >>> data that represents a real world entity, then yes, we don't have the >>> general Web "is it or isn't it physical" ambiguity and can assume that a >>> feature data identifier also and indirectly identifies the feature. That >>> still leaves a gap in expressing whether two feature data entities >>> represent the same real world entity. Perhaps we need a "sameFeatureAs" >>> predicate to address this. >>> >>> Josh >>> >>> Joshua Lieberman, Ph.D. >>> Principal, Tumbling Walls Consultancy >>> Tel/Direct: +1 617-431-6431 <%2B1%20617-431-6431> >>> jlieberman@tumblingwalls.com >>> >>> On Aug 31, 2016, at 07:29, Frans Knibbe <frans.knibbe@geodan.nl> wrote: >>> >>> Hello, >>> >>> As stated before, I don't think the httpRange-14 problem exists in our >>> domain of discourse. I think (and hope) that confusion can only occur when >>> the things that are described are digital things, or things that can be >>> transmitted over a computer network, like web pages or mail boxes. It seems >>> to me that spatial things are never that type of thing. Therefore there is >>> no reason to take precautions against possible confusion. >>> >>> That probably means +1. >>> >>> Greetings, >>> Frans >>> >>> >>> >>> On 31 August 2016 at 09:50, Jeremy Tandy <jeremy.tandy@gmail.com> wrote: >>> >>>> Thanks Rob & Clemens ... >>>> >>>> On Wed, 31 Aug 2016 at 08:30, Clemens Portele < >>>> portele@interactive-instruments.de> wrote: >>>> >>>>> +1 >>>>> >>>>> >>>>> On 30 August 2016 at 10:10:26, Jeremy Tandy (jeremy.tandy@gmail.com) >>>>> wrote: >>>>> >>>>> Hi. It would be good to close this issue out & include our collective >>>>> recommendation in the BP doc working draft. >>>>> >>>>> PROPOSAL: SDW working group recommends use of "indirect identifiers" >>>>> for spatial things >>>>> >>>>> ... I'll start the voting. >>>>> >>>>> +1 >>>>> >>>>> Jeremy >>>>> >>>>> (BTW, to make sense of the PROPOSAL you'll need to read the email >>>>> thread) >>>>> >>>>> On Fri, 26 Aug 2016 at 10:12 Linda van den Brink < >>>>> l.vandenbrink@geonovum.nl> wrote: >>>>> >>>>>> So… do we agree we can recommend indirect identifiers, or do we try >>>>>> to fix the issue with getting the correct identifier as Rob describes? >>>>>> >>>>>> >>>>>> While waiting for this I’ve updated the issue and the text referring >>>>>> to the issue in BP6. >>>>>> >>>>>> >>>>>> *Van:* Rob Atkinson [mailto:rob@metalinkage.com.au] >>>>>> *Verzonden:* woensdag 24 augustus 2016 13:56 >>>>>> *Aan:* Jeremy Tandy; Phil Archer; Linda van den Brink; Bill Roberts >>>>>> >>>>>> >>>>>> *CC:* SDW WG Public List >>>>>> >>>>>> *Onderwerp:* Re: Clarification required: BP6 "use HTTP URIs for >>>>>> spatial things" >>>>>> >>>>>> >>>>>> Hi >>>>>> >>>>>> >>>>>> Agree this is a real concern - people cant be blamed for doing the >>>>>> obvious, if dumb, thing.. >>>>>> >>>>>> >>>>>> I think we should take note of best practice in the HTML world - >>>>>> which is often to include a citable link to a resource in the rendered >>>>>> view. Or a "share" or something similar. We can also put fairly explicit >>>>>> annotation in machine-readable code - stating that the resource is about >>>>>> the URI - and even notes saying when citing this resource use the URI.... >>>>>> >>>>>> >>>>>> I'd also like to see browsers evolve to offer you the original link >>>>>> or the redirected when cutting and pasting - how hard can it be! >>>>>> >>>>>> >>>>>> Maybe we can get Ed to ask around Google Chrome team for suggestions >>>>>> on how best to handle this :-) >>>>>> >>>>>> >>>>>> Rob >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> On Wed, 24 Aug 2016 at 18:27 Jeremy Tandy <jeremy.tandy@gmail.com> >>>>>> wrote: >>>>>> >>>>>> Yes, I think so ... And we should do so if we are recommending >>>>>> "indirect identification". >>>>>> >>>>>> Jeremy >>>>>> >>>>>> On Wed, 24 Aug 2016 at 09:24, Phil Archer <phila@w3.org> wrote: >>>>>> >>>>>> Bill's comments also made me think about some of the classic >>>>>> arguments, >>>>>> such as that a lake doesn't have a last updated date and isn't 435KB >>>>>> big. Which are true, however, that kind of metadata generally comes >>>>>> from >>>>>> the server, i.e. the HTTP layer. That's an over simplification but the >>>>>> point is that it is relatively easy to avoid deliberately creating >>>>>> misleading metadata - metadata about the doc rather than the thing it >>>>>> describes - and it's also generally easy to avoid looking for that >>>>>> metadata. >>>>>> >>>>>> Is there scope for some BP advice there? >>>>>> >>>>>> Phil. >>>>>> >>>>>> On 24/08/2016 08:25, Jeremy Tandy wrote: >>>>>> > Thanks Linda. More clear examples where being "correct" (in terms of >>>>>> > avoiding uri collisions by using two distinct uris) is making >>>>>> things worse >>>>>> > because users take the wrong one! >>>>>> > >>>>>> > So, as a WG, are we content to recommend this "indirect >>>>>> identification" >>>>>> > pattern where thing & info resource identifiers are conflated? >>>>>> > >>>>>> > Bill has added some good points about how to avoid impacts of uri >>>>>> > collision- by using the (dataset) metadata to talk about licenses >>>>>> and >>>>>> > creators for the information ... >>>>>> > On Wed, 24 Aug 2016 at 07:52, Linda van den Brink < >>>>>> l.vandenbrink@geonovum.nl> >>>>>> > wrote: >>>>>> > >>>>>> >> Experience from the Netherlands: we have the id/doc pattern in our >>>>>> URI >>>>>> >> strategy, based on the Cool URIs note [8] and the ISA study on >>>>>> persistent >>>>>> >> identifiers [9]. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> That being said, same as Bill I also notice data users getting >>>>>> confused >>>>>> >> and generally using the /doc/ URI as that is the one they can >>>>>> copy from >>>>>> >> their browser address bar. This is not only casual confusion but >>>>>> also ends >>>>>> >> up in published information resources. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> You see this, for example, all over the CB-NL which is a >>>>>> vocabulary for >>>>>> >> the building sector and contains links to other Dutch standards >>>>>> such as >>>>>> >> IMGeo, an information model and vocabulary for large scale >>>>>> topography. E.g. >>>>>> >> the CB-NL concept of ‘Gebouw’ (Building) [10] links to two IMGeo >>>>>> concepts >>>>>> >> ‘Pand’ (building part) and ‘Overig Bouwwerk’ (other construction) >>>>>> using >>>>>> >> their /doc/ URIs. If you click on Pand (which doesn’t have its own >>>>>> landing >>>>>> >> page in CB-NL so I can’t include the link) you will see it >>>>>> includes the >>>>>> >> /doc/ URI as the identifier of Pand. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> This is an example where it occurs in vocabularies, but I also see >>>>>> it >>>>>> >> happen with identifiers for data instances. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> [8]: https://www.w3.org/TR/cooluris/ >>>>>> >> >>>>>> >> [9]: >>>>>> >> >>>>>> https://joinup.ec.europa.eu/sites/default/files/D7.1.3%20-%20Study%20on%20persistent%20URIs_0.pdf >>>>>> >> 10: http://ont.cbnl.org/cb/def/Gebouw >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Linda >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> *Van:* Jeremy Tandy [mailto:jeremy.tandy@gmail.com] >>>>>> >> *Verzonden:* dinsdag 23 augustus 2016 20:57 >>>>>> >> *Aan:* Bill Roberts >>>>>> >> *CC:* SDW WG Public List >>>>>> >> *Onderwerp:* Re: Clarification required: BP6 "use HTTP URIs for >>>>>> spatial >>>>>> >> things" >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Thanks Bill. Sounds very coherent ... I hoped for some responses >>>>>> such as >>>>>> >> this based on practical experience. Jeremy >>>>>> >> >>>>>> >> On Tue, 23 Aug 2016 at 19:41, Bill Roberts <bill@swirrl.com> >>>>>> wrote: >>>>>> >> >>>>>> >> ah Jeremy, you are a brave man to poke the sleeping beast of >>>>>> httpRange-14. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> But I'll get my thoughts in early, then I can tune out of the >>>>>> ensuing mail >>>>>> >> avalanche :-) >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> When publishing Linked Data about places we (at Swirrl) generally >>>>>> do the >>>>>> >> id/doc fandango, but to be honest I think data users either don't >>>>>> notice, >>>>>> >> or they get confused by it. In the applications we are working >>>>>> with (and I >>>>>> >> acknowledge that others may have different applications and >>>>>> different >>>>>> >> experiences), it wouldn't cause any problems to have a single URI, >>>>>> the 'id' >>>>>> >> URI if you like. We just don't find a need to say anything about >>>>>> the /doc/ >>>>>> >> URI. If we were starting again, I'd probably ditch the /doc/ and >>>>>> the 303 >>>>>> >> and rely on context and a little bit of documentation to make it >>>>>> clear what >>>>>> >> we mean. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> The place where we find a need to talk about creators and licences >>>>>> and >>>>>> >> modified dates is in metadata about datasets where a dataset might >>>>>> be a >>>>>> >> collection of information about a bunch of places - and we treat >>>>>> datasets >>>>>> >> as an 'information resource'. If someone requests a dataset URI we >>>>>> return a >>>>>> >> status code of 200 and the dataset metadata as the response. That >>>>>> metadata >>>>>> >> includes info on where to get all the contents of the dataset if >>>>>> you want >>>>>> >> that. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> By the way, though it's sensible and consistent, I find that the >>>>>> implied >>>>>> >> and parallel property stuff makes it more rather than less >>>>>> complicated. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Bill >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> On 23 August 2016 at 17:37, Jeremy Tandy <jeremy.tandy@gmail.com> >>>>>> wrote: >>>>>> >> >>>>>> >> All- >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Linda has done a great job of consolidating the best practices are >>>>>> use of >>>>>> >> identifiers. We have just one [1] now. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Reading though just now, it occurred to me that there's still an >>>>>> open >>>>>> >> issue about identifier assignment ... >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> W3C's Architecture of the World Wide Web constraint "URIs identify >>>>>> a >>>>>> >> single resource" [2] asserts "Assign distinct URIs to distinct >>>>>> resources" >>>>>> >> in order to avoid URI collisions [2a] which "often imposes a cost >>>>>> in >>>>>> >> communication due to the effort required to resolve ambiguities". >>>>>> >> Discussions from earlier years in UK Gov Linked Data working group >>>>>> (and >>>>>> >> elsewhere) concluded that the "real world thing" and "information >>>>>> resource >>>>>> >> that describes the real world thing" are separate resources. I >>>>>> think this >>>>>> >> is based on a (purist?) view when working with RDF of needing to >>>>>> be totally >>>>>> >> clear on "what's the subject" of each triple ... the thing or the >>>>>> document. >>>>>> >> This manifests as URIs with `id` or `doc` included somewhere to >>>>>> distinguish >>>>>> >> between the resources and some RDF triples to clarify that the doc >>>>>> resource >>>>>> >> is talking about the thing resource etc.. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> (dangerously close to "httpRange-14" [3] here ... let's avoid that >>>>>> bear >>>>>> >> trap) >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Jeni Tennison's "URLs in Data Primer" draft TAG note captures this >>>>>> >> practice in §5.3 "Publishing data" [4]: >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> ``` >>>>>> >> >>>>>> >> Publishers can help enable more accurate merging of data from >>>>>> different >>>>>> >> sites if they support URLs for each entity >>>>>> >> <https://www.w3.org/TR/urls-in-data/#dfn-entity> they or other >>>>>> sites may >>>>>> >> wish to describe, separate from the landing pages >>>>>> >> <https://www.w3.org/TR/urls-in-data/#dfn-landing-page> or records >>>>>> >> <https://www.w3.org/TR/urls-in-data/#dfn-record> that they >>>>>> publish. >>>>>> >> >>>>>> >> ``` >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Yet Architecture of the World Wide Web §2.2.3 "Indirect >>>>>> identification" >>>>>> >> [5] notes that: >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> ``` >>>>>> >> >>>>>> >> To say that the URI "mailto:nadia@example.com" identifies both an >>>>>> >> Internet mailbox and Nadia, the person, introduces a URI collision. >>>>>> >> However, we can use the URI to indirectly identify Nadia. >>>>>> Identifiers are >>>>>> >> commonly used in this way. >>>>>> >> >>>>>> >> ``` >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> This is consistent with what I recall TimBL saying at TPAC-2015 in >>>>>> regards >>>>>> >> to Vcard; come the finish, no one really cares to distinguish >>>>>> between the >>>>>> >> thing and its associated information resource. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> ... And in most cases, one can use context to determine whether a >>>>>> >> statement concerns the thing or the information resource. In those >>>>>> cases >>>>>> >> where you can't, "URLs in Data Primer" suggests some mechanisms to >>>>>> mitigate >>>>>> >> such confusion [6][7]. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> I think that in our SDW WG discussion we have concluded that we >>>>>> _are_ >>>>>> >> content to use "indirect identification" - e.g. that we use URIs >>>>>> that >>>>>> >> conflate the thing and document resource. >>>>>> >> >>>>>> >> >>>>>> >> >>>>>> >> Please can we confirm this? Assuming that indirect identification >>>>>> is >>>>>> >> >>>>>> >>>>>>
Received on Friday, 2 September 2016 22:05:47 UTC