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Re: Clarification required: BP6 "use HTTP URIs for spatial things"

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Fri, 2 Sep 2016 11:20:56 +0200
Message-ID: <CAFVDz428kocfW6DqxU+AeuisPvrm92QyCZox4WkfgvtaLNJnfg@mail.gmail.com>
To: Krzysztof Janowicz <janowicz@ucsb.edu>
Cc: Joshua Lieberman <jlieberman@tumblingwalls.com>, Jeremy Tandy <jeremy.tandy@gmail.com>, SDW WG Public List <public-sdw-wg@w3.org>
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
>> 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
>>>>> >> "approved" as best practice, then it seems prudent to add a note to
>>>>> the BP
>>>>> >> document saying "don't worry about distinguishing between thing and
>>>>> >> resource; indirect identification is fine" (etc.)
>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >> Thanks, Jeremy
>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >> [1]: http://w3c.github.io/sdw/bp/#globally-unique-ids
>>>>> >>
>>>>> >> [2]: https://www.w3.org/TR/webarch/#pr-uri-collision
>>>>> >>
>>>>> >> [2a]: https://www.w3.org/TR/webarch/#URI-collision
>>>>> >>
>>>>> >> [3]: https://www.w3.org/2001/tag/group/track/issues/14
>>>>> >>
>>>>> >> [4]: https://www.w3.org/TR/urls-in-data/#publishing-data
>>>>> >>
>>>>> >> [5]: https://www.w3.org/TR/webarch/#indirect-identification
>>>>> >>
>>>>> >> [6]: https://www.w3.org/TR/urls-in-data/#documenting-properties
>>>>> >>
>>>>> >> [7]: https://www.w3.org/TR/urls-in-data/#authoring-specifications
>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >
>>>>>
>>>>> --
>>>>>
>>>>>
>>>>> Phil Archer
>>>>> W3C Data Activity Lead
>>>>> http://www.w3.org/2013/data/
>>>>>
>>>>> http://philarcher.org
>>>>> +44 (0)7887 767755 <%2B44%20%280%297887%20767755>
>>>>> @philarcher1
>>>>>
>>>>>
>>
>
>
> --
> Krzysztof Janowicz
>
> Geography Department, University of California, Santa Barbara
> 4830 Ellison Hall, Santa Barbara, CA 93106-4060
>
> Email: jano@geog.ucsb.edu
> Webpage: http://geog.ucsb.edu/~jano/
> Semantic Web Journal: http://www.semantic-web-journal.net
>
>
Received on Friday, 2 September 2016 09:21:36 UTC

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