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

From: Frans Knibbe <frans.knibbe@geodan.nl>
Date: Thu, 1 Sep 2016 09:39:43 +0200
Message-ID: <CAFVDz421BDm-_ZJ7POM595JFQTYSzEyGeW07Qkjj-MrWNFs15g@mail.gmail.com>
To: Simon Cox <Simon.Cox@csiro.au>
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 00:56, <Simon.Cox@csiro.au> wrote:

> Ø  Now I would say the triangle is a spatial thing (not sure if it counts
> as a real world entity, but I hope we can leave the idea of 'real world'
> out of definitions anyway).
>
>
>
> This is important. In the OGC world we say that a triangle is not a real
> world entity, since you can’t touch it.
>
> You can touch something that has the shape of a triangle, but the triangle
> itself is an abstract thing.
>
>
>
> In contrast, in the GIS world, everything is subclassed from a geometry
> (point, line, polygon).
>
> This has some implementation benefits, in particular spatial indexing
> because you only have one geometry per feature and they can be sorted into
> three classes.
>

In another thread I posted the following tentative definitions of the two
core concepts that seem to be crucial for a spatial ontology:

   1. spatial things: things that have some kind of spatial presence; can
   have spatial relationships
   2. geometry: an ordered set of n-dimensional points; can be used to
   model the spatial presence of a spatial thing

Whether 'some kind of spatial presence' applies to the triangle in the
example is debatable. But that is not a bad thing. I would like it if a
spatial ontology is not too strict. For example. it should allow for cases
where the spatial thing does not exist in reality, or when the space the
object occupies is a virtual space, as in the case of the triangle. If
someone wants to share data about a triangle that only exists in an SVG
file, or about the fictional island Atlantis, and they want to model their
data as spatial data, I think that should be possible. Trying to build
impenetrable semantic walls around definitions of spatial data is a battle
that will have little gain and can never be won, I think.

Still, if people will use our spatial ontology to model their data, they
will have to accept the premises that go with it. One of which could that
there can not be confusion between the URI of a spatial thing and the URI
of data describing that spatial thing.

Regards,
Frans



>
>
> *From:* Frans Knibbe [mailto:frans.knibbe@geodan.nl]
> *Sent:* Thursday, 1 September 2016 12:21 AM
> *To:* Joshua Lieberman <jlieberman@tumblingwalls.com>
> *Cc:* Jeremy Tandy <jeremy.tandy@gmail.com>; SDW WG Public List <
> public-sdw-wg@w3.org>
> *Subject:* Re: Clarification required: BP6 "use HTTP URIs for spatial
> things"
>
>
>
>
>
>
>
> On 31 August 2016 at 13:42, 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.
>
>
>
> I hope we can broaden that assumption, that the assertion still holds even
> if we are not talking about feature data representing real world entities.
>
>
>
> Let's look at a border case: I am drawing a triangle in Inkscape and I
> save it as a *.svg file. I publish the file on the web, so it has a URI.
> Now I would say the triangle is a spatial thing (not sure if it counts as a
> real world entity, but I hope we can leave the idea of 'real world' out of
> definitions anyway). The SVG object in the file is the geometry describing
> the spatial thing. I think that only if we understand the SVG file to be
> the spatial thing we get into trouble. I might want to state that the file
> has a certain size and that the triangle has a certain area. It would be
> funny if I used the same URI for both statements. So I would need to have a
> different URI for my triangle. Could that be all?
>
>
>
> 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.
>
>
>
> Yes, that is what the Subject equality
> <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SubjectEquality>
> requirement is about. So the BP document is expected to say something about
> that.
>
>
>
> Regards,
>
> Frans
>
>
>
>
>
> 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
> @philarcher1
>
>
>
>
>
Received on Thursday, 1 September 2016 07:40:17 UTC

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