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Re: Splitting vs. Interpreting

by Alan Ruttenberg-2 :: Rate this Message:

(apologies for the resend, Sean - missed the cc's in the first response)

On Tue, Jun 16, 2009 at 3:23 PM, Sean B. Palmer <sean@...> wrote:

You write about ambiguous and specific references here:

http://dbooth.org/2007/splitting/

When I worked on EARL in 2002, we had to solve httpRange-14, and we
did it in a practical way which your splitting document reminds me of.

We might want to evaluate a tool of some kind in EARL, say the W3C
Validator. But then we didn't know whether validator.w3.org was the
tool itself or a page about the tool. That's httpRange-14 in a
nutshell, before it was “solved” with the 303 hack.

So what we did was this:

<http://validator.w3.org/> earl:tool _:Validator .

The clever bit is that the earl:tool property says: if the subject is
a Document (i.e. an IR), then the object is the Tool described by that
document; whereas if the subject is a Tool, then the object is simply
the same thing as the subject.

This isn't quite the same idea as splitting (which is more problematic). Here the ambiguity is maintained due to not completely constraining the interpretation of http://validator.w3.org/. Essentially, you are asserting, as a consequence of the use of earl:tool, that http://validator.w3.org/ is of type unionOf(tool document). However, assuming that tool and document are disjoint, you can't use http://validator.w3.org/ both in one place which forces it to be of type document (e.g as the target of foaf:page), and another which forces it to be a tool (e.g. http://validator.w3.org/ :runUnderOS :linux). Doing so would lead to a logical consistency.

Dave's splitting proposal, OTOH, lands up recapitulating the class/instance distinction with another mechanism, one which doesn't offer the same support for reasoning that that the existing SW stack offers.

What I like about your solution is that you at least admit that documents and services are different sorts of things, instead of using a term inconsistently. If *everyone* used http://validator.w3.org/ in this way, it could work.

But if everyone is to use the same scheme, it would seem better to me to define a new type that made directly clear the nature of http://validator.w3.org/ as being a sort of service which can do two different things a) respond with a report about conformance to RDF syntax of a supplied document and b) respond with a page that documents how (a) works. Then have two *unambiguous* properties a) earl:tool that relates http://validator.w3.org/ to an entity whose type is tool, and b) foaf:page that relates to a document. It would be helpful to document, as well, that the tool (b) generates a new instance of document, each time it is "run".

-Alan

And as you can imagine, this is extensible to interpreting ambiguous
resources in all kinds of ways. Now the TAG finding says that it's
removed a certain level of ambiguity, but there are other ambiguities
one might want to resolve when a page 303s and then still doesn't
define carefully what's at the end of it. So the EARL method is much
more practical.

You might also want to think a bit harder about statements such as
“there is no architectural need for Person and IR to be considered
disjoint”. Consider if you were using Facebook and it started
conflating people with groups and games and so on. But of course
people break the rules of the web until they matter, and since there's
no Semantic Web User Agent this rule doesn't matter.

I'm not saying that the TAG finding should be canned because you can
use the kind of interpretation properties that I've described as a way
around it. The point is rendered moot by various architectural
problems. But you ought to compare the 2002 and 2009 architectural
solutions carefully.

--
Sean B. Palmer, http://inamidst.com/sbp/

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