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

From: Krzysztof Janowicz <janowicz@ucsb.edu>
Date: Thu, 1 Sep 2016 19:33:31 -0700
To: Rob Atkinson <rob@metalinkage.com.au>, Jeremy Tandy <jeremy.tandy@gmail.com>, Joshua Lieberman <jlieberman@tumblingwalls.com>, Frans Knibbe <frans.knibbe@geodan.nl>
Cc: SDW WG Public List <public-sdw-wg@w3.org>
Message-ID: <d1b81f30-52b4-93d9-800e-16e82c1ea606@ucsb.edu>
Hi Rob,

>  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.

I assume you mean  so-called information and non-information resources, 
right?

> So the information content is always URI + some client-defined context 
>  -> a resource that the server believes meets the context requirements.
>
> At the very least U -> { R1, R2,R3...}

I am a bit lost here. Are we talking about content negotiation?

> -> can be seen as some type of property relationship - so this 
> behaviour can be automated or also stated in a useful way
>
> U hasRepresentation R1

Hmm. That sounds very unusual to me (most likely I am simply 
misunderstand it). URIs do *not* represent something, they signify (like 
in semiotics). For instance, 
dbpedia.org/resource/Santa_Barbara,_California does not represent Santa 
Barbara nor does http://dbpedia.org/page/Santa_Barbara,_California . The 
URL dbpedia.org/resource/Santa_Barbara,_California is the globally 
unique identifier of the place on the surface of the Earth that we refer 
to 'Santa Barbara, CA'. If I utter the statement 'I work in Santa 
Barbara', then this 'Santa Barbara' is not a representation of the place 
but a pointer. I can also have empty pointers in the sense that there is 
no such thing to which it is pointing. Atlantis is (most likely ;-)) an 
example.

> So - if we have two FeatureTypes (Vert.Obstruction) and (Nav..) then 
> we have two scenarios we need to cover:
>
> 1) U -> {R1, R2)
> 2) U1 -> R1, U2 -> R2, U1 = U2
>
> In summary - as an implementer who now understands the probIem I have 
> a small number of questions:
>
> 1) in the latter case is BP to declare U1 owl:sameAs U2? If not - what 
> is the predicate ?
>
> 2) what is the appropriate predicate for the  U predicate R1 ?
>
> 3) How do I share the context (i.e. those reified bindings of U to 
> R1...n) so a client can understand them

How can 1) be the case? One URI points to one specific entity/resources, 
not two. the different feature types do not matter here. RDF is not 
about representation, it is about statements. OWL, of course, would be a 
different story.

>
> 2) what is the appropriate predicate for the  U predicate R1 ?

If U is a URI and R1 is some entity, then URI is simple the globally 
unique identifier for that entity. Also keep in mind that RDF is about 
sets of statements, nothing more.

Interesting discussion, btw.

Krzysztof




On 08/31/2016 03:24 PM, Rob Atkinson wrote:
>
> Important we have this in depth discussion and reach consensus - 
> because its impossible to expect a wider audience to arrive at a 
> usefully common view without guidance.
>
> This stuff is out there, so its not a theoretical discussion. but some 
> of the practices conflate things in a way that makes data hard to 
> integrate.
>
> There are a couple of practical implications I havent seen fully 
> addressed, yet would need to be highlighted IMHO:
>
>  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.   What is important to recognise here is that the 
> relationship between U and R is mediated by conneg... In the case of 
> the UK Linked Data example, it may be further mediated by additonal 
> parameters within the Web architecture.
>
> So the information content is always URI + some client-defined context 
>  -> a resource that the server believes meets the context requirements.
>
> At the very least U -> { R1, R2,R3...}
>
> -> can be seen as some type of property relationship - so this 
> behaviour can be automated or also stated in a useful way
>
> U hasRepresentation R1
>
> or perhaps reified
>
> { subject U, object R1, predicate hasRepresentation, type 
> aFeatureType, label "X', dct:hasFormat "image/svg" }
>
> The reified case makes it obvious that the "client defined context" 
> can be matched to the properties of the relationship - however this 
> logic is just as likely to be implemented in the conneg or API layer, 
> thats a contract between client and server which is part of the 
> broader Web architecture - for now let us focus on whether the 
> functionality required can be met by the available information...
>
> now if  U1 -> R and U2 -> R then both U1 and U2 may have the same set 
> of properties in this case
>
> X owl:SameAs Y  states that the properties of X apply to Y and vice 
> versa. There are other implications here as well
>
> he value constraintowl:hasValue 
> <http://www.w3.org/TR/2004/REC-owl-semantics-20040210/#owl_hasValue>is 
> a built-in OWL property that links a restriction class to a value V, 
> which can be either anindividual 
> <https://www.w3.org/TR/owl-ref/#Individual>or adata value 
> <https://www.w3.org/TR/owl-ref/#Datatype>. A restriction containing 
> a|owl:hasValue|constraint describes a class of all individuals for 
> which the property concerned has at least one value/semantically/equal 
> to V (it may have other values as well).
>
> NOTE: for datatypes "semantically equal" means that the lexical 
> representation of the literals maps to the same value. For individuals 
> it means that they either have the same URI reference or are defined 
> as being the same individual (seeowl:sameAs 
> <https://www.w3.org/TR/owl-ref/#sameAs-def>).
>
> So I beleive they key thing here is to provide guidance to those 
> unfamiliar with the semantics underpinnings to not break things and 
> given them a simple way forward.
>
> So - if we have two FeatureTypes (Vert.Obstruction) and (Nav..) then 
> we have two scenarios we need to cover:
>
> 1) U -> {R1, R2)
> 2) U1 -> R1, U2 -> R2, U1 = U2
>
> In summary - as an implementer who now understands the probIem I have 
> a small number of questions:
>
> 1) in the latter case is BP to declare U1 owl:sameAs U2? If not - what 
> is the predicate ?
>
> 2) what is the appropriate predicate for the  U predicate R1 ?
>
> 3) How do I share the context (i.e. those reified bindings of U to 
> R1...n) so a client can understand them
>
> If we cannot nail down the terms to use now, then I believe we need to 
> state in the BP that a mechanism needs to be chosen to address these 
> specific concerns according to the principles of re-use - but I also 
> suggest we flag this as a critical "must solve" issue for the 
> communities we would suggest pointing users to.
>
> Rob
>
>
> On Thu, 1 Sep 2016 at 03:13 Krzysztof Janowicz <janowicz@ucsb.edu 
> <mailto:janowicz@ucsb.edu>> wrote:
>
>     Thanks for the clarification.
>
>
>     On 08/31/2016 09:22 AM, Jeremy Tandy wrote:
>>     @josh
>>
>>     > Is the triangle spatial data or a graphic with drawing
>>     instructions that assumes a certain technology? If 100 people
>>     print out the SVG, there is really nothing to indicate that the
>>     underlying entity is the same on each piece of paper, just that
>>     the same instructions were used, unless we want to get into
>>     trademark issues.
>>
>>     This seems to be getting away from the main topic. Unless you
>>     object, can I pull us back?
>>
>>     @Krzysztof
>>
>>     Apologies if my terminology is confusing.
>>
>>     I was trying to say that <owl:sameAs> indicates that two
>>     identifiers (URIs, in this case
>>     <http://example.com/sar/features/vo/EDY> and
>>     <http://example.org/maritime/navaid/2650253>) refer to the same
>>     entity (Eddystone Lighthouse). You said it much better than me.
>>
>>     The term "representation" was drawn from @josh's email text; in
>>     which he meant "Eddystone Lighthouse seen as a vertical
>>     obstruction" and "Eddystone Lighthouse seen as a maritime
>>     navigation aid".
>>
>>     >there is no need for such a class [whose members are both
>>     vertical obstructions and maritime navigation aids] (which you
>>     can define if you really want to, but it could lead to a
>>     combinatorial explosion)
>>
>>     I agree. This is what I've seen with Linked Data implementations
>>     - which means that "sameRealWorldEntityAs" is not required.
>>
>>     Hmmm. I hope I'm not confusing myself and everyone else.
>>
>>     Jeremy
>>
>>     On Wed, 31 Aug 2016 at 17:02 Joshua Lieberman
>>     <jlieberman@tumblingwalls.com
>>     <mailto:jlieberman@tumblingwalls.com>> wrote:
>>
>>>         On Aug 31, 2016, at 10:20 AM, Frans Knibbe
>>>         <frans.knibbe@geodan.nl <mailto:frans.knibbe@geodan.nl>> wrote:
>>>
>>>
>>>
>>>         On 31 August 2016 at 13:42, 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.
>>>
>>>
>>>         I hope we can broaden that assumption, that the assertion
>>>         still holds even if we are not talking about feature data
>>>         representing real world entities.
>>>
>>>         Let's look at a border case: I am drawing a triangle in
>>>         Inkscape and I save it as a *.svg file. I publish the file
>>>         on the web, so it has a URI. Now I would say the triangle is
>>>         a spatial thing (not sure if it counts as a real world
>>>         entity, but I hope we can leave the idea of 'real world' out
>>>         of definitions anyway). The SVG object in the file is the
>>>         geometry describing the spatial thing. I think that only if
>>>         we understand the SVG file to be the spatial thing we get
>>>         into trouble. I might want to state that the file has a
>>>         certain size and that the triangle has a certain area. It
>>>         would be funny if I used the same URI for both statements.
>>>         So I would need to have a different URI for my triangle.
>>>         Could that be all?
>>
>>         Is the triangle spatial data or a graphic with drawing
>>         instructions that assumes a certain technology? If 100 people
>>         print out the SVG, there is really nothing to indicate that
>>         the underlying entity is the same on each piece of paper,
>>         just that the same instructions were used, unless we want to
>>         get into trademark issues.
>>
>>>             That still leaves a gap in expressing whether two
>>>             feature data entities represent the same real world
>>>             entity. Perhaps we need a "sameFeatureAs" predicate to
>>>             address this.
>>>
>>>
>>>         Yes, that is what the Subject equality
>>>         <http://w3c.github.io/sdw/UseCases/SDWUseCasesAndRequirements.html#SubjectEquality>
>>>         requirement is about. So the BP document is expected to say
>>>         something about that.
>>>
>>>         Regards,
>>>         Frans
>>>
>>>
>>>             Josh
>>>
>>>             Joshua Lieberman, Ph.D.
>>>             Principal, Tumbling Walls Consultancy
>>>             Tel/Direct: +1 617-431-6431 <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
>>>>>                                 >> "approved" as best practice,
>>>>>                                 then it seems prudent to add a
>>>>>                                 note to the BP
>>>>>                                 >> document saying "don't worry
>>>>>                                 about distinguishing between thing and
>>>>>                                 >> resource; indirect
>>>>>                                 identification is fine" (etc.)
>>>>>                                 >>
>>>>>                                 >>
>>>>>                                 >>
>>>>>                                 >> Thanks, Jeremy
>>>>>                                 >>
>>>>>                                 >>
>>>>>                                 >>
>>>>>                                 >> [1]:
>>>>>                                 http://w3c.github.io/sdw/bp/#globally-unique-ids
>>>>>                                 >>
>>>>>                                 >> [2]:
>>>>>                                 https://www.w3.org/TR/webarch/#pr-uri-collision
>>>>>                                 >>
>>>>>                                 >> [2a]:
>>>>>                                 https://www.w3.org/TR/webarch/#URI-collision
>>>>>                                 >>
>>>>>                                 >> [3]:
>>>>>                                 https://www.w3.org/2001/tag/group/track/issues/14
>>>>>                                 >>
>>>>>                                 >> [4]:
>>>>>                                 https://www.w3.org/TR/urls-in-data/#publishing-data
>>>>>                                 >>
>>>>>                                 >> [5]:
>>>>>                                 https://www.w3.org/TR/webarch/#indirect-identification
>>>>>                                 >>
>>>>>                                 >
>>>>>


-- 
Krzysztof Janowicz

Geography Department, University of California, Santa Barbara
4830 Ellison Hall, Santa Barbara, CA 93106-4060

Email: jano@geog.ucsb.edu
Webpage: http://geog.ucsb.edu/~jano/
Semantic Web Journal: http://www.semantic-web-journal.net
Received on Friday, 2 September 2016 02:34:08 UTC

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