On Apr 13, 2007, at 3:10 PM, Ed Barkmeyer wrote:
When the URI is a reference to a Web page (full stop), the
resource is the web page, and by extension, the information content of the web
page.
I think of the page and its information content as being
separate.
From an ontological point of view, I may also want to distinguish
the content from its external representation, if that was your point. But the Web does not make that distinction. Put another way, the Web consciously
manages external representations of information, and leaves the abstraction of
content to the reader. The whole idea
of the Semantic Web is to provide standard external representations for some
orderly abstraction of content, in order to facilitate search.
I find it important to distinguish the location of the
information from its content, which was my point. So perhaps we are talking past each other.
But the definition of URI (IETF RFC 2396) says it identifies
a "resource".
For example, I can make statements about the style of the
page display, the server where the <html> tags reside, the provenance
information for the page. These are
all separate from the information content of the page.
We have now identified several distinguishable concepts:
2) the presentation structure (web page)
3) the information content
4) a formal description of the content
5) the "provenance metadata" for the content
6) the provenance metadata for the presentation
7) the provenance metadata for the presentation in that
place
And we could easily make a model (ontology) for these things
and their relationships:
place(1) conveys presentation(2)
presentation(2) conveys content(3)
content(3) has formal description(4)
content(3) has provenance of content(5)
presentation(2) has provenance of presentation(6)
place(1) has provenance of site content(7)
Further we note that there are other possibilities. In particular,
place(1) provides service(8)
service(8) permits access to presentation(2)
RFC 2396 is pretty clear that a URL identifies a place(1)
full stop, and indicates a means of access to whatever is at that place. From our would-be ontology above, what is
thus addressed is either a presentation/document or a service.
By comparison, RFC 2396 says that a URI identifies a
"resource". And all of
(2),(4),(5),(6),(7) and the service (8) are distinct resources that may be
found at the *same site*. (I think the
Web view is that content(3) is only accessible through its presentation(2).) It follows that each of them should have a
distinct URI. Those URIs may be
distinct URLs in their own right, or they may all incorporate a common URL and
each have a distinct fragment identifier.
Since a URL always identifies a place, if the distinct
resources have distinct URLs, our model above needs some additions:
place(1) conveys formal description(4)
place(1) conveys provenance of content(5)
place(1) conveys provenance of presentation(6)
place(1) conveys provenance of site content(7)
One place can convey some or all of (2),(4),(5),(6),(7),(8),
but when one place conveys more than one of them, each has a distinct URI whose
"fragment identifier" distinguishes the "component". And by convention, in those cases, the URI
with no fragment identifier (the simple URL) conveys either (2) or (8). It is also possible that we have a (9),
which is a web page that is a container for (2),(4),(5),(6),(7), delivered as a
single resource.
Note that our model is starting to get rather messy.
This is why Tim Burners-Lee says you need to impose some
discipline on your site. The problem
is that several different conventions have emerged (including not imposing any
discipline), and there are no reference standards.
In a somewhat different vein, I wrote:
I have argued with TBL before that URIs that are URLs
confuse WHAT something is with WHERE it is. And
it is only an acceptable idea when that relationship is required to be 1-to-1. The idea of identifiers is that you can
test for equal. When the same thing
can be in multiple places, unequal doesn't tell me anything, which is annoying,
especially when tools think unequal to the expected value means unusable. And when the same place can hold different
things, equal doesn't tell me anything, which defeats the purpose.
What you are saying is it doesn't serve the purpose you have
in mind, not that it doesn't serve other purposes quite well. One could say the success of the Web shows
a real value.
Whoa! I fully agree
that URLs locate lots of useful and functionally different things, just as
postal addresses do. But if today it's
a bank and tomorrow it's a laundry or a residence or a casino, what
"resource" is being "identified"?
What I said was that if the content to which a URI refers
changes radically from day to day, the URI doesn't identify "an
information resource" in any useful sense. And thus the idea that the URI identifies
something different from a location is false.
If the purpose of a URI is to denote content, function, behavior, as
distinct from location, some one of those has to be consistent over time. A bulletin board and a pulpit are just
locations.
(I wonder how many XML tools would break if the namespace
URL for XML Schema pointed to a local copy of the specification... Is the W3C URI THE name or A name for the
XML Schema specification?)
This is where provenance comes in. It is THE URI if you believe W3C to be the
authoritative source.
1. The location of
the document
2. The identity of
the document as the one issued by the authoritative source.
Example: The authoritative
source for the Oxford Dictionary of English is presumably in Oxford, England,
but I can find the document at my public library.
All of the copies of the ODE have the same designation, but
you can find copies in lots of places. So
if I point you to a place where you can find it, that has nothing to do with
the authoritative source.
But my example was wrong. The
xmlns reference is to the "namespace URI", which is the required
*identifier* for the specification. The
tool is free to get a copy from anywhere it likes. So if I put another URL there, it may be a
location of a copy of the specification, but it is NOT the *identifier*, and
the tool should fail. It is exactly as
if I referred to the "Peoria Public Library's dictionary" instead of
the ODE.
The webhead idea is that you will always go to the URL,
fetch the resource, and use it. The
idea that a tool has been pre-programmed to support that *content*, and, in
conducting a web-based transaction, this might require the tool to fetch and
compare two 10MB files to determine whether they are *versions of* the same
specification, is beyond their hobbyist view of the Internet.
So what metadata do you need in place to support your use? How do you want to create and maintain that
metadata? Will you make it available
for others to use?
Ah, now we are talking about what "responsible
management" of referenceable resources might be. This is the kind of discipline that the
WebDAV folks have worked on, and there is a "widely accepted" scheme
for life cycle management of documents. The
trouble is that it is widely accepted among the various organizations involved
in making document and metadata standards, but those folks operate and
influence less than 1% of websites. It
does mean that publishers, and standards organizations, and library websites
will probably use it.
Everything is a resource to someone, as it should be. What we want to be able to do is
differentiate resources so we use the one(s) most suitable for our needs.
Exactly. But unless
there are common conventions for that differentiation, all we have is a bunch
of disorganized resources labeled according to hundreds or thousands of
incompatible schemes, most of which are not very good or very useful. Google has built a successful enterprise on
the failure of the Web, and its principal resources, to address that problem. And there are many who believe that that
also is as it should be.
IMO, the problem is that Internet is still the big city of
the Middle Ages. We know how to build all kinds of buildings and we have a lot
of demand for them and a lot of construction of various kinds and qualities
going on. But no one is responsible
for much of it, we have no civil engineering discipline, we have no land use
planning, we have random patchworks of streets, we are carrying the water on
foot in buckets from the most convenient well, we have no police force and no
fire brigade, we have sewage problems, crime problems and frequent plagues. Some communities thrive and some die out,
and we don't really understand why. And
yet people keep coming here, because there is education, and jobs, and
entertainment, and money to be made. Ultimately,
technology enabled us to get control of it, and fires and plagues forced us to. But it took 7 centuries. I hope the Internet experience is shorter.
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