On 5/3/07, Geoffrey Sneddon <[EMAIL PROTECTED]> wrote: On 2 May
2007, at 16:53, James M Snell wrote:
The meaning is application dependent. For instance, Lotus
Connections uses a category scheme value "http://www.ibm
.com/xmlns/prod/sn/type", which when used with a set of
specific terms (e.g. "message", "bookmark", "chat", etc) has
a very specific meaning in the Lotus Connections product.
If it's application specific, I assume the attribute itself has no
semantics. I fail to see how this is useful for aggregators
whatsoever, as its content could mean almost anything.
Application specific things should probably be left to
namespaces where attributes can be defined with actual semantics.
The problem here is that something is missing in Atom's set of category
attributes. (This was brought up long ago.) For an aggregator to make sense
of a category within a particular schema, it must either have knowledge of
the specific schema or it must have a mechanism to do inference about the
similarity of items in different schemas -- at least one of which that it
understands. Given this, what we see is that the Atom category tag (and many
other tagging schemes) really should be much more like what is defined in
XTM[1]. The missing, secret sauce that is in XTM (and Topic Maps generally)
that is NOT in Atom categories is the "Published Subject
Indicator<http://www.topicmaps.org/xtm/index.html#desc-subject-indicator>."
The PSI is a schema independent URI for the particular concept or thing that
is being tagged. Given a subject indicator, it is possible to map between
ontologies. For instance, I can have a German ontology that contains the
word "Buch" and an English ontology that contains the word "Book" and I can
link them both together if we can agree that the Published Subject Indicator
(resource) for these things is: http://en.wikipedia.org/wiki/Book.
Similarly, two ontologies, one which refers to "pro-choice" and the other to
"baby-killing" can be linked if both entries link to an ontology independent
published subject indicator.
Often, there is great agreement between ontology developers concerning the
objective identity of the things that they classify. "What you're talking
about" isn't the issue. It is "What you say about it" that is the problem.
For instance, you may build a list "Great US Presidents" and someone else
might build a list of "Worst National Leaders." It is likely that you'll
both agree completely that any references to "George Bush" in either list
refer to precisely the same individual but, while you agree on who you're
talking about, you'll probably disagree on Bush's proper place within each
ontology. In a case like this, you should use a Published Subject Indicator
to allow mapping between the two ontologies. The PSI is neutral, the
position within the ontology is not...
In general, I believe the fact that we don't seem to understand the
potential uses of Published Subject Indicators is one of the biggest things
holding back tagging systems and systems for doing interchange between
ontologies... XTM shows the way to do this usefully...
Atom's category element should have a "subject-indicator" attribute in
addition to label and schema.
bob wyman
[1] http://www.topicmaps.org/xtm/index.html
