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

From: Jeremy Tandy <jeremy.tandy@gmail.com>
Date: Fri, 02 Sep 2016 14:16:24 +0000
Message-ID: <CADtUq_1EoZAhju+TvOgH58o_roj5GUvkBgfNLcuqBcKzODGtDQ@mail.gmail.com>
To: Frans Knibbe <frans.knibbe@geodan.nl>, Krzysztof Janowicz <janowicz@ucsb.edu>
Cc: Joshua Lieberman <jlieberman@tumblingwalls.com>, SDW WG Public List <public-sdw-wg@w3.org>
@simon:

> https://g.co/kg/m/013qr8?_view=vertical-obstruction is the URI for a
particular representation, possibly a graph

Yes.

> _*within**_* the graph denoted <
https://g.co/kg/m/013qr8?_view=vertical-obstruction> you will usually *
*not** find this URI used as the subject of an statements providing
properties of a vertical obstruction (or navigation aid), but rather *
*will** find a bunch of statements with the subject <
https://g.co/kg/m/013qr8>

Yes.

And furthermore, I think that few people will care to name the
representation / graph at all.

@rob:

Re-reading the email thread this morning, I wonder if I misinterpreted your
concern?

Prompted by Jano's email [1] I see that you originally stated:

> One mechanism in widespread use is that the URI for the 'thing' redirects
to a URL for a resource about the thing. Lets call these U & R.

Now, by using "indirect identification" I was hoping that we would not
routinely need to define separate URIs (URLs?) for "thing" and "description
of the thing". I thought that we'd agreed that in the general case this was
fine?

At the risk of making another (incorrect) cognitive jump, I wonder if
you're looking at the problem examined in your Spatial Identifier Reference
Framework (SIRF) work? e.g. where you mint an identifier for a spatial
thing _because_ you discovered a data source that talked about that spatial
thing. Furthermore, multiple data sources may all talk about the same
spatial thing. The data exists already and SIRF tries to link these
different information resources, and therefore provides a pathway for users
to discover related information by browsing those links.

Hence, looking at your cited example, I can see that <
http://environment.data.gov.au/water/id/catchment/100862> is linked to a
number of information resources such as a getFeature request URL for a WFS
endpoint (albeit that that doesn't seem to be working) ... so I can see why
you were interested in understanding the Link relation (such as
`describedby`) that might be used here.

SIRF is way more sophisticated than the typical HTTP 303 redirect - I think
because you anticipate linking to _many_ information resources and are
trying to given people the choice about which one the server at <
http://environment.data.gov.au/water> provides ...

In my email sent yesterday [2] I noted that the Linked Data API also
provides a mechanism for users to select a particular "representation" (or
"views") of a resource - using a SPARQL Construct statement to pull out the
required statements from the underpinning triple store. SIRF is different;
the information is federated across a number of service endpoints.

Both SIRF and LDA seek to address, at least in part, the limitations of
content negotiation which were identified in Geo4web-testbed Topic 4:
"Content negotiation based on media types insufficient" [3]. Erik Wilde's
"profile" Link Relation Type proposal (RFC 6906) [4] is related to this
problem too I think.

What I'm struggling with is understanding whether these are (widely
adopted) best practices or intelligent point solutions? Within the scope of
the BP deliverable, I can include best practices (!) or identify a lack of
best practice for a (well understood) requirement. Based on previous
guidance from @phila, we have the mandate to write additional W3C Notes for
related subjects if we deem it appropriate; perhaps this would be a good
way to progress any intelligent point solutions that are addressing gaps in
best practice?

Proposals welcome.

Jeremy


[1]: https://lists.w3.org/Archives/Public/public-sdw-wg/2016Sep/0048.html
[2]: https://lists.w3.org/Archives/Public/public-sdw-wg/2016Sep/0018.html
[3]: http://geo4web-testbed.github.io/topic4/#h.n0gkernttzw0
[4]: https://tools.ietf.org/html/rfc6906

On Fri, 2 Sep 2016 at 13:02 Jeremy Tandy <jeremy.tandy@gmail.com> wrote:

> @frans:
>
> > 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.
>
> In a perfect world, all statements from all sources made about the same
> spatial thing would be true. Sadly, we don't live in a perfect world. Some
> things change (e.g. the lighthouse may fall down and become much shorter,
> or be rebuilt larger - the first incarnation built by Winstanley was only
> 18m tall) and sometimes we just make errors (in this case, I wrongly
> reported that Eddystone Lighthouse is 41m tall- but this is the _focal
> height_ of the light itself ... Wikipedia [1] indicates that this fourth
> incarnation of Eddystone Lighthouse is 49m tall).
>
> Care always needs to be taken when combining information from different
> sources to determine if it is valid and/or correct - for example, by
> looking at the date of publication or whether it is from a trustworthy
> source.
>
> <owl:sameAs> is appropriate to relate URIs used to identify Eddystone
> Lighthouse - the construction that has existed in (more or less) the same
> place on the Earth's surface since 1698. ... <owl:sameAs> would not be
> appropriate to relate URIs that explicitly identify Winstanley's Eddystone
> Lighthouse (the first incarnation) and Douglass' Eddystone Lighthouse (the
> 4th and current incarnation); these are different spatial things ... but
> they may be related to the general Eddystone Lighthouse using some other
> predicate.
>
> Jeremy
>
> [1]: https://en.wikipedia.org/wiki/Eddystone_Lighthouse
>
> On Fri, 2 Sep 2016 at 10:20 Frans Knibbe <frans.knibbe@geodan.nl> 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
>>>> 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" identif
>>>>>>>
>>>>>>>
Received on Friday, 2 September 2016 14:17:08 UTC

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