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More EARL (0.9) Issues

From: Sean B. Palmer <sean@mysterylights.com>
Date: Wed, 16 May 2001 17:14:36 +0100
Message-ID: <05fe01c0de23$6f26a880$4eda93c3@z5n9x1>
To: <w3c-wai-er-ig@w3.org>
1) Granularity of results. This was raised a while ago, in the 12
February teleconference [1], and Len followed it p with an action item
to write some more about it, which he did [2]. However, some of this
work was "forgotten" when drafting EARL 0.9, and I'm not sure we have
a good enough range of expression rating-wise.

At the moment, I'm moving towards explicitly enumerating certain
classes, using "oneOf" in DAML. However, this wouldn't allow for
extensibility afterwards, so we could say that the main class is
comprised of a disjoint union of two sub classes, one of which is made
by ERT - an explicit enumeration, and the other is for public use to
add terms that they want a certain processor to use. This reminds me
very much of the extra parameter entities in XHTML m12n, that allow
people to extend, for example, the common attributes. Hmm... neat
little analogy.

2) Still no feedback on the "building RDF statements by creating an
intersection of DAML restrictions on the reification properties",
although I expect some from Libby today. I think I'll just go with my
gut and say that it's correct, although Wendy, you can chase it up if
you want.

Let's try to explain what's going on here:-

What we want to say is that we have a statement (a triple) that is
comprised of specific parts. In EARL, we are creating (for example) a
earl:Evaluation, which is made up of the parts "earl:Assertor",
"earl:asserts", and "earl:Assertion". EARL Assertion is also a
statement, but we can ignore that for now. What you can say (what we
do say in 0.9) is that when you use an "earl:asserts" property, it has
to be used in an earl:Assertor, and the object must be an
earl:Assertion, but this has two disadvantages: a) it's too
constraining, what if I want to use earl:asserts on something else? b)
there is no way to say that this particular statement is an
earl:Evaluation.

Now, DAML has a method of putting restrictions on certain terms, so
for example, you can say that "earl:Assertor" is a rdfs:subClassOf a
restriction on the property "earl:asserts" to "earl:Assertion". In
other words, when, and only when, earl:asserts is being used upon an
earl:Assertor, the object of it must be earl:Assertion. So far so
good, but what if we applied this to the entire statement?

In RDF, to say what a statement is comprised of, you have three
properties - rdf:subject, rdf:predicate, and rdf:object. So, for
example, where you have the triple:-

     :John :loves :Mary .

The rdf:subject of that statement is ":John", the rdf:predicate is
":loves", and the rdf:object is ":Mary". In other words:-

   [ rdf:Statement;
     rdf:subject :John;
     rdf:predicate :loves;
     rdf:object :Mary ] .

O.K., now remember the DAML restriction stuff? What we could say is
that in the case of an earl:Evaluation, the rdf:subject of it can only
ever be an *instance* of earl:assertor, the rdf:predicate can only
ever be *exactly* earl:asserts, and the rdf:object can only ever be an
instance of earl:Assertion. These statements in RDF are:-

   [ daml:onProperty rdf:subject;
     daml:toClass earl:Assertor ]
   [ daml:onProperty rdf:subject;
     daml:hasValue earl:asserts ]
   [ daml:onProperty rdf:subject;
     daml:toClass earl:Assertion ]

Unfortunately, we have to make the statements separately - look at the
confusion it would cause if you had two onProperty arcs - you wouldn't
know which one goes where! Thankfully, DAML gives us a method to say
that our particular class is comprised of all of these restrictions -
it's the intersection of these:-

   earl:Evaluation daml:intersectionOf
     ([ daml:onProperty rdf:subject;
        daml:toClass earl:Assertor ]
      [ daml:onProperty rdf:subject;
        daml:hasValue earl:asserts ]
      [ daml:onProperty rdf:subject;
        daml:toClass earl:Assertion ]) .

Ta da (round of applause please). Notes: if there could be other
things that have these particular restrictions, then we would say that
earl:Evaluation is a sub class of the intersection of these
restrictions, but I think if it looks/smells/feels like an
earl:Evaluation, then it is one, so I'm just going to say it's the
intersection.

You can do a similar thing to earl:Assertion.

3) Does the above method make the restriction on earl:asserts
obsolete? I'm not too sure about the stability of the above still, so
I would be inclined to say that we might as well include the
semantics, even if they can be inferred. My concern with the RDF model
is that although instances of it can have the power of semantic
transformations and so forth, if there are holes in the model, it's
difficult to patch up.

4) Are there any other sub classes of earl:Assertor that we need to
note? At the moment, we only have earl:Person. Maybe we could allow
earl:Tool here as well (or possibly earl:AssertingTool). Do we have to
enumerate this? Could we use a similar method to 1)?

5) I think we should change the "hasName", "hasEmail" and so forth
into just "name", "email" and so on. Aaron et al. had a big discussion
on using noun and verb clauses on SWAG-Dev, and no real consensus was
reached (I actually argued for the "hasX", so I'm being a bit
hypocritical here).

6) Do we need to include other properties that humans could have other
that email address and so on? Could we import some of the terms used
in P3P?

7) More prose for the terms, please. At the moment, just looking
through the schema, it is next to impossible to work out hat each of
the terms is for, just by name. We need to agree on the prose and best
practices for the terms - it's not something one of us can just hack
up.

8) How do we express ranges of dates on NonUniqueTestSubjects? I want
to say that this applies to my particular Web page, which was in
action between two particular dates, or even more complicated, between
a certain set of dates. We need some equivalent of a "fromDate" and
"toDate" mechanism... hmm:-

   :MyPage a earl:NonUniqueTestSubject;
      :dateRange [ :fromDate "2001-03-05";
                          :toDate "2001-03-17" ] .

If so, there's no way that we can use dc:date for this. I think we
should really consider the future with dc:date - why use it explicitly
in the instances when we can just mess about with it on the schema
side?

Note that ":dateRange" above could then just become "earl:date", which
would be a (disjoint?) union of earl:Date and earl:DateRange. Hmm...
I'm not sure about all that, because of the restrictions we have on
the cardinality of date properties... earl:DateRange would be used on
earl:NonUniqueTestSubject, multiple earl:Date's would be used on
earl:NonUniqueTestSubject, and single earl:Date's would be used on
earl:UniqueTestSubject.

To express multiple date ranges, you'll have to use DAML in the
instances (which I wanted to avoid - maybe we could use another
equivalent?), so you could have:-

   :MyCoolPage a earl:NonUniqueTestSubject;
      :dateRange [ daml:intersectionOf
                              ([ :fromDate "2001-03-05";
                                  :toDate "2001-03-17" ]
                               [ :fromDate "2001-03-21";
                                  :toDate "2001-03-25" ]) ] .

Or, rather...

   :MyCoolPage a earl:NonUniqueTestSubject;
      earl:date [ daml:intersectionOf
                              ([ earl:fromDate "2001-03-05";
                                  earl:toDate "2001-03-17" ]
                               [ earl:fromDate "2001-03-21";
                                  earl:toDate "2001-03-25" ]) ] .

That's a pretty neat bit of hacking, that.

[1] http://lists.w3.org/Archives/Public/w3c-wai-er-ig/2001Feb/0088
[2] http://lists.w3.org/Archives/Public/w3c-wai-er-ig/2001Feb/0097

--
Kindest Regards,
Sean B. Palmer
@prefix : <http://webns.net/roughterms/> .
:Sean :hasHomepage <http://purl.org/net/sbp/> .
Received on Wednesday, 16 May 2001 13:18:23 GMT

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