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

Re: Working on glossary

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 10 Sep 2001 19:52:52 -0500
Message-Id: <v04210110b7c30a3d2a0c@[205.160.76.173]>
To: Graham Klyne <Graham.Klyne@Baltimore.com>
Cc: w3c-rdfcore-wg@w3.org
>At 05:14 PM 9/5/01 +0200, Martyn Horner wrote:
>
>>An RDF Glossary
>>
>
>[...]
>
>>Entity
>>
>>
>>The world (and the world of information that it encloses) contains 
>>a vast number of `entities' - things we talk about and think about. 
>>Many have names and words in human languages, some have no name but 
>>can be referred to in passing.
>> [RDFT&C]
>> Anything which exists or has existed. Note that RFC2396 uses this 
>>term in a more restricted sense, to mean some data represents some 
>>aspect of a Web Resource.
>>
>>
>>[MH] Actually [RFC2396] doesn't attempt to define `entity'.
>>
>
>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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Received on Monday, 10 September 2001 20:51:35 EDT

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