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

From: Rob Atkinson <rob@metalinkage.com.au>
Date: Thu, 01 Sep 2016 23:21:00 +0000
Message-ID: <CACfF9LxC9+g434ZB5C1UcV2SAu8M0dvAf0r2f0Uo69o8oEbUVg@mail.gmail.com>
To: Jeremy Tandy <jeremy.tandy@gmail.com>, Rob Atkinson <rob@metalinkage.com.au>, janowicz@ucsb.edu, Joshua Lieberman <jlieberman@tumblingwalls.com>
Cc: Frans Knibbe <frans.knibbe@geodan.nl>, SDW WG Public List <public-sdw-wg@w3.org>
>
>
> > Do we recommend [use of <foaf:isPrimaryTopicOf>], or leave it free
>
> This is just one of many properties that might be used. Another is the
> describedby Link Relation defined by POWDER-DR [1]. Given that POWDER-DR is
> a W3C REC, this would give it the edge for me ... and it's available for
> use beyond the realms of RDF given its inclusion in the IANA Link Relations
> registry [2].
>
> There may be others that the working group prefer.
>
>
Well - he're the nub of the issue :-)  IMHO this is the point at which most
implementers will either be grateful for a direction or give up in disgust
because we've specified something that doest suit, or left them dangling.

I like the IANA link - but also it feels bad to leave practice like the UK
LOD stuff "hanging" with a counter proposal.  How can we reconcile
maximising the value of existing stuff with recommended "better practice"




> All that said, I see the majority of folks being happy to work with the
> (indirect) identifiers for their spatial things / features without
> concerning themselves with identified representations.
>
> Jeremy
>
> [1]: https://www.w3.org/TR/powder-dr/#appD
> [2]: http://www.iana.org/assignments/link-relations/link-relations.xhtml
>
> On Thu, 1 Sep 2016 at 23:06 Rob Atkinson <rob@metalinkage.com.au> wrote:
>
>>
>> Circling in on a resolution here I hope :-)
>>
>> from what I am seeing -
>>
>> we need to make a very clear statement that geo "Features" are things
>> that have comparable URIs - but instances of "FeatureTypes" are
>> representations that are related. These representations are properties of
>> the Feature that may be combined using  using owl:sameAs between the
>> Features, but not the representation (FeatureType) instances
>>
>> There is practice 'in the wild" to use foaf as a vocabulary for the
>> relationship.  Do we recommend this, or leave it free.  Do we specify that
>> whatever relationship is used is a subProperty of foaf:primaryTopicOf  ?
>>
>> And finally, there is probably no established best practice for providing
>> discovery of available bindings - and we should flag this as something that
>> should be addressed - a missing BP against requirements
>>
>> There is evidence its at least feasible conforming to the vocabuary reuse
>> BP -   for example a graph based mainly on VoiD can be made available as
>> an extra representation using the IANA "alternates" relationshp  c.f. in
>> the SIRF project  (
>> http://environment.data.gov.au/water/id/catchment/100862?_view=alternates&_format=html -
>> notwithstanding that the resources are woefully maintained now :-( Very sad
>> as there was even a link checker that exploited this view available! )
>>
>> Rob
>>
>> On Fri, 2 Sep 2016 at 07:42 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) .
>>>
>>> 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"
>>>>>>>
>>>>>>>
Received on Thursday, 1 September 2016 23:21:46 UTC

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