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[ISSUE-57] Drawback to Parallel Properties

From: Sean B. Palmer <sean@miscoranda.com>
Date: Wed, 29 Oct 2014 14:26:48 +0000
Message-ID: <CAH3-oEdx21+ZY6Y88Ns9MEqiaVbOzvKUjCTCqgkp26AyN8=KyA@mail.gmail.com>
To: "www-tag@w3.org" <www-tag@w3.org>
This is a minor comment on a technique described in:

Providing and Discovering URI Documentation
Editor's Draft 2 February 2012
http://www.w3.org/2001/tag/awwsw/issue57/20120202/

Section 4.2 describes a method called parallel properties, which has
been independently invented on several occasions.

The method consists of creating properties that are designed to refer
to the "designated subject" of a document, which bears some relation
and may even be equivalent to its foaf:primaryTopic.

To expand such references, we also need to give a name to the
relationship between the asserted property and the inferred property.
In the example graph given in the section, these are eq:epicenter and
"has epicenter". I shall refer to this relation as the "direct
property".

That is to say, this example from the section:

  <http://example/eq018> eq:magnitude 6.9.
  <http://example/eq018> eq:epicenter <geo:37.040,-121.877>.

Implies the following:

  <http://example/eq018> pp:designatedSubject [
    [ is pp:directProperty of eq:magnitude ] 6.9;
    [ is pp:directProperty of eq:epicenter ] <geo:37.040,-121.877>
  ].

There is a significant drawback to this method. It is that it appears
that you can use non-parallel properties on the same subject, whereas
in fact this leads to inconsistencies. A good example of a common
non-parallel property that someone may attempt to use is owl:sameAs:

  <http://example/eq018> owl:sameAs
    <http://example2/document.rdf#eq018> .

This statement would cause all sorts of inferential chaos. In the
earthquake example such incorrect inferences may not be regarded as
especially harmful, but there are alternative scenarios in which they
would be, such as where a document has another document as its
designated subject. In that case, the inferential chaos caused by
owl:sameAs would make the metadata of both documents
indistinguishable.

To recap, the properties eq:magnitude and eq:epicenter in the example
appear to have the nature of non-parallel properties, and would cause
confusion unless specifically documented as a pp:ParallelProperty
instances, with the characteristics of parallel properties being
widely known. This problem is similar to spoofing. There is no
requirement preventing it in the list of desiderata (Section 1.1).

Note that parallel property analogues to non-parallel properties can
be made. In the case of owl:sameAs, for example, we could say:

  { ?s pp:designatedSubjectSameAs ?o } =>
    { ?s pp:designatedSubject [ owl:sameAs ?o ] } .

And also:

  { ?s pp:sameDesignatedSubjectAs ?o } =>
    { ?s pp:designatedSubject
        [ owl:sameAs [ is pp:designatedSubject of ?o ] ] }.

But this approach is not very straightforward.

-- 
Sean B. Palmer, http://inamidst.com/sbp/
Received on Wednesday, 29 October 2014 14:27:16 UTC

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