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

From: Krzysztof Janowicz <janowicz@ucsb.edu>
Date: Sun, 4 Sep 2016 20:31:05 -0700
To: Simon.Cox@csiro.au, rob@metalinkage.com.au, frans.knibbe@geodan.nl
Cc: jlieberman@tumblingwalls.com, jeremy.tandy@gmail.com, public-sdw-wg@w3.org
Message-ID: <b3f644e1-c28f-bab5-1ce0-9986cd81f525@ucsb.edu>
*Hi,


*
>
> *Rob* wrote:
>
> Øconsider two resources with URIs R1 and R2
>
> Ø
>
> ØR1 ns:dateEdited 12/1/2001
>
> Ø
>
> ØR2 ns:dateEdited 6/6/2006
>
> Ø
>
> ØR1 owl:sameAs R2  then leads to ambiguity regarding the value of the 
> functional property ns:dateEdited
>

Note that this is not a owl:sameAs issue. I think it is very important 
to distinguish between co-reference resolutions (using owl:SameAs, 
skos:closeMatch,...) and data conflation (data fusion). owl:SameAs 
handles co-reference resolution. Data fusion is still an open research 
issue (despite tons of work in the DB community). The fact that 
ns:dateEdited may be defined as a functional property in some ontology 
will also have no effect on the RDF triples as such.

Best,
Krzysztof



On 09/04/2016 05:04 PM, Simon.Cox@csiro.au wrote:
>
> *Rob* wrote:
>
> Øconsider two resources with URIs R1 and R2
>
> Ø
>
> ØR1 ns:dateEdited 12/1/2001
>
> Ø
>
> ØR2 ns:dateEdited 6/6/2006
>
> Ø
>
> ØR1 owl:sameAs R2  then leads to ambiguity regarding the value of the 
> functional property ns:dateEdited
>
> Where R1 and R2 are representations or descriptions of a (real-world) 
> thing, possibly a graph of RDF triples.
>
> However, in a separate part of the thread, *Jeremy* wrote:
>
> Øfew people will care to name the representation / graph at all.
>
> In other words, the URIs R1 and R2 are usually not treated with much 
> respect. So it is unlikely that we would be in the business of making 
> sameAs statements about these.
>
> Simon
>
> *From:*Rob Atkinson [mailto:rob@metalinkage.com.au]
> *Sent:* Saturday, 3 September 2016 8:05 AM
> *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>
> *Subject:* Re: Clarification required: BP6 "use HTTP URIs for spatial 
> things"
>
> 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 
> <mailto: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 <mailto: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
>                     <mailto: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
>                     <http://example.com/sar/features/vo/%22%3EEDY%3C/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
>                     <mailto: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
>                         <tel:%2B1%20617-431-6431>
>
>                         jlieberman@tumblingwalls.com
>                         <mailto:jlieberman@tumblingwalls.com>
>
>
>                         On Aug 31, 2016, at 07:29, Frans Knibbe
>                         <frans.knibbe@geodan.nl
>                         <mailto: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
>                             <mailto:jeremy.tandy@gmail.com>> wrote:
>
>                                 Thanks Rob & Clemens ...
>
>                                 On Wed, 31 Aug 2016 at 08:30, Clemens
>                                 Portele
>                                 <portele@interactive-instruments.de
>                                 <mailto:portele@interactive-instruments.de>>
>                                 wrote:
>
>                                     +1
>
>                                     On 30 August 2016 at 10:10:26,
>                                     Jeremy Tandy
>                                     (jeremy.tandy@gmail.com
>                                     <mailto: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
>                                         <mailto: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
>                                             <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
>                                             <mailto: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
>                                                 <mailto: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
>                                                     <mailto: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
>                                                     <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
>                                                     <mailto: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
>                                                     <mailto: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
>                                                     <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
>                                                     >>
>


-- 
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 Monday, 5 September 2016 03:31:39 UTC

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