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John Cowan said: "On this basis, "John Cowan" is a non-URI name of *me*,
whereas mailto:cowan@ccil.org"; is a URI name of *one of my mailboxes*."
Is 'A URI name' an oxymoron when applied to a URL? There is a danger of
getting names and references mixed up here (not to speak of 'definite
descriptions').
RFC 2396 says: "A Uniform Resource Identifier (URI) is a compact string of
characters for identifying an abstract or physical resource."
And later:
"A URI can be further classified as a locator, a name, or both. The term
"Uniform Resource Locator" (URL) refers to the subset of URI that identify
resources via a representation of their primary access mechanism (e.g.,
their network "location"), rather than identifying the resource by name or
by some other attribute(s) of that resource. The term "Uniform Resource
Name" (URN) refers to the subset of URI that are required to remain globally
unique and persistent even when the resource ceases to exist or becomes
unavailable."
So a URL is an identifier by location not by name. I would call this a
reference.
'John Cowan' is a name of John Cowan (though not a URN). The name of the
mailbox cowan@ccil.org is 'cowan@ccil.org' not mailto:cowan@ccil.org. The
mailto is a reference to that mailbox (part of which happens to be its
name).
In other words, the fact that mailto:cowan@ccil.org is a URL not a URN makes
it a reference (by location) rather than a name.
Does this matter? I think it does. A reference to an object is not the same
as its name (this is the difference between an object's 'handle' and its
'key' in EJB terms). I can de-reference a reference to get the object, but I
can't de-reference a name (in general). On the other hand, references to an
object are specific to the way the de-referencing is done whereas names are
independent of the way they are de-referenced (and they persist across
object instantiations). They are therefore used for different purposes.
It seems as though the problem with namespaces is that they use a method for
referencing resources to name abstract resources.
John F Schlesinger
SysCore Solutions
-----Original Message-----
From: John Cowan [mailto:cowan@mercury.ccil.org]
Sent: 04 March 2002 12:01
To: Bent Rasmussen
Cc: xml-dev@lists.xml.org
Subject: Re: [xml-dev] Assumptions about URIs
Bent Rasmussen scripsit:
> - "Does the URI 'http://www.w3.org' identify an
> organisation called W3C or a location on the Web?"
For informal purposes, it can refer to either, just as informally
I can be called either "John Cowan" or "mailto:cowan@ccil.org";.
For RDF/TM purposes, when it is necessary to make rigorous
distinctions, then there are two possible answers:
- A URI means what the owner of the authority-part (DNS name) says it
means. On this basis, "John Cowan" is a non-URI name of *me*,
whereas "mailto:cowan@ccil.org"; is a URI name of *one of my
mailboxes*.
- The meaning of a URI must be inferred from the statements made
about it. In this case we would have to look to what has been said.
--
John Cowan http://www.ccil.org/~cowan cowan@ccil.org
To say that Bilbo's breath was taken away is no description at all. There
are no words left to express his staggerment, since Men changed the language
that they learned of elves in the days when all the world was wonderful.
--_The Hobbit_
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