W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > September 2001

Re: Working on glossary

From: Graham Klyne <Graham.Klyne@MIMEsweeper.com>
Date: Tue, 11 Sep 2001 11:38:41 +0100
Message-Id: <5.1.0.14.2.20010911111021.03881980@joy.songbird.com>
To: pat hayes <phayes@ai.uwf.edu>
Cc: w3c-rdfcore-wg@w3.org
At 01:52 AM 9/11/01 +0100, pat hayes wrote:
>Oh dear. That simply does not make sense. Look, there are two notions here.
>One is the thing with an identity, more traditionally called the thing
>denoted; examples include web sites, books, human beings, corporations, etc.
>. Another is the conceptual mapping or correspondence between the name and
>that first thing, sometimes called the denotation mapping. These are not,
>and cannot possibly be, the same thing. So RFC2396 is just plain confused.

[Full message below]

Oh dear, indeed ;-)

I'll not try and respond directly to your points (yet), but see if I can 
skirt around them..


Problem statement:

The web currently contains many things, identified by URIs, that correspond 
to ideas like "the current weather".  I think this is something that makes 
the web truly valuable -- the ability to deliver dynamic information.  If 
RDF cannot describe these things then I think it falls very short of the 
goal to be able to describe all things that are "on the Web".


Some tangential background:

One of the challenges of functional programming, in its strictest form in 
which all values are immutable, is its use in applications that deal with 
inherrently dynamic things (text editors, real-time control, etc.).  The 
approach that I have seen adopted is to treat such things as sequences of 
values, or time-varying functions.  Coupled with techniques like lazy 
evaluation that only evaluate values as they are required, a program can 
represent and handle such possibly-infinite values.


Possible solution?

(This may be a horrible abuse of a new trick, but I must try...)

The functional programming trick seems not dissimilar to the 
relational-extension trick used in the MT denotation of RDF 
predicates.  Can it also be applied to the denotation of resources?

So, a "resource" is the thing identified by a URI.  Why not have the idea 
of a resource extension that corresponds to the set of entities that can be 
retrieved via a resource, where each entity is a static sequence of octet 
data?  (At this stage, for the purpose of testing the resource extension 
idea, I've deliberately stuck to things that can actually be retrieved on 
the web, and left unspecified any correspondence there may be between the 
data and other real-world objects.)  Then, the resource can correspond to 
the current weather forecast, but its extension includes the set of all 
weather forecasts for all times;  the particular member of that extension 
one retrieves depends on when the retrieval is performed.

It seems to me that this treatment of resources is allowed by, and 
orthogonal to the current model theory, because it still provides a fixed 
denotation for each URI, just one a that is more complex than originally 
envisaged.  It also seems, to me, to capture something of the intent of 
RFC2396.

#g
--

At 01:52 AM 9/11/01 +0100, pat hayes wrote:
> >
> > This is true -- Though RFC2396 does draw a clear distinction between
> > "resource" and "entity":
> >
> >       Resource
> >          A resource can be anything that has identity.  Familiar
> >          examples include an electronic document, an image, a service
> >          (e.g., "today's weather report for Los Angeles"), and a
> >          collection of other resources.  Not all resources are network
> >          "retrievable"; e.g., human beings, corporations, and bound
> >          books in a library can also be considered resources.
> >
> >          The resource is the conceptual mapping to an entity or set of
> >          entities, not necessarily the entity which corresponds to that
> >          mapping at any particular instance in time.  Thus, a resource
> >          can remain constant even when its content---the entities to
> >          which it currently corresponds---changes over time, provided
> >          that the conceptual mapping is not changed in the process.
> >
> >
>Oh dear. That simply does not make sense. Look, there are two notions here.
>One is the thing with an identity, more traditionally called the thing
>denoted; examples include web sites, books, human beings, corporations, etc.
>. Another is the conceptual mapping or correspondence between the name and
>that first thing, sometimes called the denotation mapping. These are not,
>and cannot possibly be, the same thing. So RFC2396 is just plain confused.
>
>BTW, it is even more confused that this, since neither of these notions
>(entity denoted and denotation mapping) have got anything particularly to do
>with time and change, and the introduction of a temporal distinction in the
>second paragraph seems to confuse denotation - the mapping from a
>representing or naming symbol to the thing it denotes or names - with some
>notion of a temporally unchanging referent which somehow 'corresponds'
>(whatever that means) to a changing value. The phrasing " the entity which
>corresponds to that mapping at any particular instance in time" is
>incoherent and meaningless. The last sentence is nonsense: if the thing
>identified by the mapping changes, then *of course* the mapping has changed,
>since the mapping *is* the relationship between the names (or referring
>expressions) and the things 'identified' by the mapping..
>
>I don't think there is any point it trying to 'rescue' this prose. It is too
>broken to be useful.
>
>
> > Hence, I have a problem with:
> >
> >
> >       Resource
> >
> >                       The universe in which RDF operates is seen as a
> > potentially huge collection of `resources'.
> >
> >
> >                       Resources are the identifiable items in the world,
> > the contact points between you and the world of data. They are `entities'
> > as we need to refer to them, fixed for a short time while we talk about
> > them.
> >
> >
> >
> > I think it is important to keep the clear distinction between "resource"
> > and "entity" so that resources like "the current weather report" don't tie
> > us up in knots.
> >
> >
>They are already tied up in knots. That phrase is meaningless in an
>extensional language, since it has an implicit "now" in it, which is an
>indexical. If URIs have an implicit reference to the time of use built into
>their meaning, then *any* model theory for *any* language which uses URIs
>will need to be based on something like a modal semantics which explicitly
>mentions temporally possible worlds. That could be done, but it gets us into
>a minefield of complexity (what kind of temporal model do we assume?
>Discrete or continuous? Based on points or intervals? Deterministic or
>branching? Etc.)
>
>The RDF model theory as it stands simply does not support the notion of an
>URI meaning 'the current weather report'. There is no notion of 'current'
>or 'now' or 'at the time of accessing' in the semantics.  At any given
>moment, a URI might denote the weather report at that moment, but if that
>gets changed then the meaning of the URI gets changed as well. Changing the
>content of a weather-report URI is a genuine change, not merely an update to
>an ongoing temporally-relative 'tensed' meaning.
>
>
>
>
>
> >                       A typical resource would be a unit of data on the
> > Web such as a page or a significant segment of a page. Equally another
> > person, an organization or anything else that you would wish to point at
> > out there in this universe can be referred to as a `resource'. The
> > significant characteristic is the identifiable nature of resources, that
> > they have for whatever period of time an identity which makes them
> > distinguishable.
> >
> >
> >                       [RDFT&C] May refer to an RDF resource or a Web
> > Resource. Some resources may be both. In discussion of RDF, this term is
> > often used to mean RDF Resource.
> >                       [RDFM&S:introduction]
> >                       A resource may be an entire Web page; such as the
> > HTML document "http://www.w3.org/Overview.html" for example. A resource
> > may be a part of a Web page; e.g. a specific HTML or XML element within
> > the document source. A resource may also be a whole collection of pages;
> > e.g. an entire Web site. A resource may also be an object that is not
> > directly accessible via the Web; e.g. a printed book. Resources are always
> > named by URIs plus optional anchor ids (see [URI]). Anything can have a
> > URI; the extensibility of URIs allows the introduction of identifiers for
> > any entity imaginable.
> >
> >
> >                       [RDFM&S:glossary]
> >                       An abstract object that represents either a
> > physical object such as a person or a book or a conceptual object such as
> > a color or the class of things that have colors. Web pages are usually
> > considered to be physical objects, but the distinction between physical
> > and conceptual or abstract objects is not important to RDF. A resource can
> > also be a component of a larger object; for example, a resource can
> > represent a specific person's left hand or a specific paragraph out of a
> > document. As used in this specification, the term resource refers to the
> > whole of an object if the URI does not contain a fragment (anchor) id or
> > to the specific subunit named by the fragment or anchor id.
> >
> >
> >                       [Jena] Some entity. It could be a web resource such
> > as web page, or it could be a concrete physical thing such as a tree or a
> > car. It could be an abstract idea such as chess or football. Resources are
> > named by URIs.
> >
> >
> >                       [N3] That identified by a Universal Resource
> > Identifier (without a "#"). If the URI starts "http:", then the resource
> > is some form of generic document.
> >
> >       Web Resource
> >
> >                       Resources which have their identity by nature of
> > their accessibility on the World Wide Web are sometimes distinguished as
> > `Web Resources'. To make this identification, we may have to chose one
> > aspect of this entity's contact with the Web - for an organization: a
> > particular Web page, for a person: an email account, etc.
> >                       [RDFT&C]
> >                       Anything that is identified by a URI
> >
> >
> >
> > Further ammunition for the distinction between an RDF resource and a web
> > resource:
> >
> > [[[
> > When making a reference, such as a hypertext link, we don't just refer to
> > a
> > resource. Well, we can, but we can also refer to a particular part of or
> > view
> > of a resource.
> >
> >
>Oh dear. That also doesn't make sense to me. What does it mean to refer to a
>'particular view' of something, rather than refer to it?
>
>
> > The string which, within the document, defines the other end of
> > the link has two parts. It has the identifier of the document as a whole,
> >
> >
> >
>So a URI is an identifier of a *document* ?? But I thought that we were
>working on the understanding that URIs denote *things*, not just documents.
>
>
>
> > and
> > then optionally it has a hash sign "#" and a string representing the view
> > of
> > the object required.  This suffix is called a fragment identifier.  (Even
> > though it doesn't represent necessarily a fragment of the document: it
> > could
> > represent how the document should be viewed.)
> >
> >
>How about representing things that have nothing to do wth documents?
>
>
> > ]]]
> >  -- http://www.w3.org/DesignIssues/Model.html
> >
> > [[[
> > Fragment identifiers for RDF identify concepts
> >
> > The semantic web has information about anything. The fragment identifier
> > on
> > an RDF (or N3) document identifies not a part of the document, but
> > whatever
> > thing, abstract or concrete, animate or innanimate, the document describes
> > as
> > having that identifier.
> >
> >
>Which flatly contradicts the previous quote. Sigh.
>
>Pat
>---------------------------------------------------------------------
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>phayes@ai.uwf.edu
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>
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------------------------------------------------------------
Graham Klyne                    MIMEsweeper Group
Strategic Research              <http://www.mimesweeper.com>
<Graham.Klyne@MIMEsweeper.com>
------------------------------------------------------------
Received on Tuesday, 11 September 2001 06:42:57 EDT

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