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RE: exploring ambiguity via the "something-which-has" URI scheme

From: Hammond, Tony (ELSLON) <T.Hammond@elsevier.com>
Date: Tue, 6 May 2003 12:20:10 +0100
Message-ID: <54A600C436EA694581B93E4BD4D4788A06B7398C@elslonexc004.wins.epress.co.uk>
To: "'Patrick.Stickler@nokia.com'" <Patrick.Stickler@nokia.com>, sandro@w3.org
Cc: uri@w3.org, GK@ninebynine.org, phayes@ai.uwf.edu

Hi Patrick:

Perhaps a better link for OpenURL (sic) would be

	http://library.caltech.edu/openurl/Public_Comments.htm

which provides relevant links to the Part 1 and Part 2 draft documents. "The
OpenURL Framework for Context-Sensitive Services" is an ANSI/NISO draft
standard (Z39.88-2003) which last week entered a 6-month Trial Use following
a period of Public Comments. The OpenURL Framework describes a generic means
for bundling contextualized identifier/metadata packages for mediating
services. This draft standard defines a suite of transports for these
packages using HTTP/S GET/POST methods - the OpenURL. The architecture is
designed to be extensible to new application domains and to use new
transport methods - eg SOAP.

Tony


Tony Hammond

Advanced Technology Group, Elsevier Ltd
32 Jamestown Road, London, NW1 7BY, UK

<tel:+44-20-7424-4445>
<mailto:t.hammond@elsevier.com>



> -----Original Message-----
> From: Patrick.Stickler@nokia.com [mailto:Patrick.Stickler@nokia.com]
> Sent: 05 May 2003 10:55
> To: sandro@w3.org
> Cc: uri@w3.org; GK@ninebynine.org; phayes@ai.uwf.edu
> Subject: RE: exploring ambiguity via the "something-which-has" URI
> scheme 
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: ext Sandro Hawke [mailto:sandro@w3.org]
> > Sent: 02 May, 2003 19:29
> > To: Stickler Patrick (NMP/Tampere)
> > Cc: uri@w3.org; GK@ninebynine.org; phayes@ai.uwf.edu
> > Subject: Re: exploring ambiguity via the "something-which-has" URI
> > scheme 
> > 
> > 
> > 
> > Patrick Stickler writes
> > > This appears to be a URI scheme for expressing constellations
> > > of properties defined for an anonymous node (and not very unlike
> > > open-URIs).
> > 
> > I've never heard of "open-URIs" and I can't find anything 
> relevant in
> > google.  Pointer?  It certainly seems similar to the "secure URI"
> > thread [1] going on in this list .  I was invoking RDF as a 
> way to to
> > jump to the end of the arms-race for more general languages.
> 
> Sorry. The name is "Open URL" (not URI). 
> 
> C.f. http://www.dlib.org/dlib/march01/vandesompel/03vandesompel.html
> 
> > > I would think that what such URIs really denote would be the
> > > *class* of all resources which match those specified properties.
> > 
> > Ah, the ambiguity of natural language.  Yes, from my 
> examples and the
> > way I named the scheme that would be a perfectly reasonable
> > interpretation.  As would the idea you feared, that I was 
> proposing a
> > URI scheme where URIs did not have a single denotation.  
> But I defined
> > in otherwise.  I thought my text made that clear.
> > 
> > One the first point:
> > 
> > Let's call the two versions x-scheme-1 and x-scheme-2.  Each
> > x-scheme-1 URI denotes something for which the given RDF graph is
> > true.  Each x-scheme-2 URI denotes the class of things for which the
> > given RDF graph is true.  
> > 
> >    
> > <x-scheme-1:foaf_mbox='connolly@w3.org';defpre(foaf_,http://xm
> > lns.com/foaf/0.1/)>
> > 
> > denotes Dan Connolly, while
> > 
> >    
> > <x-scheme-2:foaf_mbox='connolly@w3.org';defpre(foaf_,http://xm
> > lns.com/foaf/0.1/)>
> > 
> > denotes the (singleton) class of things which are Dan Connolly.
> > 
> > Assuming the empty graph (always true) is written as the 
> empty string,
> > and we can conclude:
> > 
> >    <x-scheme-1:> a rdf:Resource.      # it's something, but we
> > 				      # have zero clue which thing
> > 
> >    <x-scheme-2:> a rdfs:Class.        # we at least know 
> it's a class
> > 
> > 
> > I'm defining my strawman something-which-has URI scheme to be
> > x-scheme-1.  
> 
> What happens then, when there occur more than one thing that satisfy
> the properties you specify in the URI?
> 
> 
> > (There's a naming challenge in making this clear in the scheme name.
> > Any grammatical phrase, like "individual-such-that" can 
> still be read
> > as "(the class of) individual(s) such that".  Recent programming
> > conventions make the distinction using letter-case: must of us would
> > guess "redThing" denotes an individual which is red, "RedThing"
> > denotes a class of red things.  I also like the convention 
> "redThings"
> > would denote a collection of individuals which are red, but 
> sometimes
> > redThingList or redThingSet is necessary.)
> > 
> > One the second point: Consider the noun phrase "a red 
> thing" in "I am
> > holding a red thing in my hand."  That noun phrase could denotes any
> > of a huge variety of things, but I'm using it to refer to a very
> > specific physical object.  URIs always refer to a specific thing,
> > even when no one happens to know anything about that thing.
> 
> Well, that seems to be the crux of a long running debate. 
> 
> If a URI is overloaded, then it does not refer to a specific thing.
> 
> Even if a specific SW agent considering a specific RDF graph might
> presume (and IMO rightly so) that a given URI denotes a specific
> thing, the source of its knowledge as captured in that graph may
> have been syndicated from two or more sources which ultimately
> disagree about the actual denotation of the URIs used, but that
> disagreement is not and cannot be reflected in the URIs themselves.
> 
> Thus, you may "this red thing" and I may say "this red 
> thing" but those may very well be different red things, yet your
> URI scheme will result in the overloading of a URI reflecting
> "a red thing" and thus result in confusion.
> 
> Better to just use a uuid: URI to denote the specific resources
> and then describe them accordingly. If if is ever determined that
> they are the same thing, we can use owl:sameAs to equate the two
> UUID denoted resources.
> 
> UUIDs are nice in that they provide all the flexibility of anonymous
> nodes but without them actually being anonymous. In fact, I once
> suggested that we have a special URI scheme for RDF anonymous nodes
> which is essentially identical to the uuid: scheme but called anon:
> and which would be used to denote anonymous nodes, rather than
> using just local system-specific identifiers. 
> 
> Anyway....
> 
> > > I think that it is (or should be) a fundamental presumption that,
> > > within the scope of the S/Web, a given URI consistently denotes
> > > a single thing.
> > 
> > Agreed.  I think Graham and Pat and you and I are in 
> violent agreement
> > on this on this list.
> 
> Yes. And alot of the violence is my fault, being insane enough to 
> conduct discussions regarding logic in semantics using only the
> English language rather than more precise mathematical terms ;-)
> 
> > But there are some tricky edge cases, which is what I am trying to
> > flesh out.  In particular, while agents may act as if a URI had one
> > true interpretation, they are only acting: we cannot, in general,
> > communicate interpretations.  At best, we can arbitrarily constraint
> > interpretations; that seems to be good enough for both humans and
> > machines.
> 
> Right.
> 
> But in communicating about things, it seems to be best practice
> to choose names that have the greatest change of being recognized
> as widely as possible with the same denotation and have the
> smallest chance of being overloaded.
> 
> So, having a URI scheme based on simply listing the minimal set
> of distinguishing features of a resource, per *your* system,
> seems to have an extraordinaryly high risk of colliding with
> other uses of that same URI but with a different denotation.
> Thus, your URI scheme, while logically valid, does not seem to
> reflect the above best practice regarding the selection of URIs
> to denote resources for the global interchange of knowledge
> between arbitrary systems.
> 
> It also seems to hide knowledge about the resource in the URI
> itself, rather than making it explicitly visible to agents
> as statements about the resource denoted by the URI.
> 
> > > So if you tried to define a URI scheme that could
> > > intentionally be used to provide for overloading of denotation,
> > > I would consider that to be in conflict with the fundamental
> > > S/Web architecture.
> > 
> > I think it would also be in fundamental conflict with web
> > architecture, but ... I'm not sure how to phrase it for 2396bis.  My
> > last attempt [2] was ignored by everyone.  :-)
> > 
> > Here's another attempt, changing the basic definition of a URI.
> > Again, this goes somewhere near the beginning; exact glue can wait.
> > 
> >    Each URI is a string which conforms to URI syntax and which names
> >    something.  The naming relationship gives the URI its primary
> >    utility, allowing it to be transmitted in the place of something
> >    else.  There is no restriction on what kind of thing (real,
> >    imaginary, physical, conceptual, ...) can be named by a URI, but
> >    all such things are called "resources".  
> > 
> >    For a URI to be used effectively, the parties using it in
> >    communication often need to share a notion of which resource it
> >    names, but this commonality of knowledge does not need to be
> >    complete to be effective. In particular, human parties 
> will tend to
> >    associate considerable real-world knowledge with the named
> >    resource, while software agents will simply maintain the facts
> >    about it suitable to their purpose.  In many cases there will be
> >    some ambiguity in communication using URIs because of incomplete
> >    sharing of knowledge about what is named by each URI, but this
> >    ambiguity can often be reduced as far as necessary.
> 
> Here you seem to be doing the same thing that Pat seems to be doing,
> lumping together without distinction the agreement about the URI to 
> resource mapping and agreement about the qualities of the resource
> to which the URI refers.
> 
> So, while not all parties will be concerned with, nor even agree
> about all knowledge globally asserted (somewhere) about the resource
> in question, they still need to agree that they are talking about
> the same thing -- i.e. that the URI in question refers to one and
> only one thing and they agree what that thing is.
> 
> Humans can make and test such agreements. SW agents must simply
> presume that such an agreement is in force and valid when it
> merges two RDF graphs from different sources.
> 
> 
> >    [ maybe say something about renaming and about indexical 
> URIs like
> >    my.example.com?  something about GoodURIs having a long-term
> >    consensus of meanings.... ]
> > 
> >    In addition to serving as a name, each URIs can also serve as a
> >    message, conveying information about the named resource.  The
> >    language of the message is identified by the URI's 
> scheme part, and
> >    to use the information encoded into the URI, an agent must
> >    recognize the scheme name and understand the corresponding
> >    language.  A common case is for the URI text to convey 
> the network
> >    address of a server which can communicate 
> authoritatively about the
> >    resource.
> > 
> > Or something....   Do you agree with what is stated there, 
> even if you
> > disagree it has the best wording?
> 
> Well, if you are using the URI itself to convey knowledge about
> the resource denoted, I would ideally hope to see as part of that
> URI scheme some component which reflects a globally unambiguous
> (non-overloaded) denotation. Perhaps adding a manditory component
> to the URI scheme which is a UUID, to ensure that naming collisions
> do not occur.
> 
> Patrick
> 
Received on Tuesday, 6 May 2003 07:22:13 GMT

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