Subject: atom:category@scheme

From: Geoffrey Sneddon <[email-masked]>
Date: Tue, 1 May 2007 18:57:41 +0100

@scheme is defined as "The 'scheme' attribute is an IRI that  
identifies a categorization scheme". Is this therefore like atom:id,  
in that it is an identifier, and the actual IRI is meaningless.

- Geoffrey Sneddon

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From: James M Snell <[email-masked]>
Date: Tue, 01 May 2007 14:28:06 -0400

The IRI has meaning, it just may not be dereferenceable.

- James

Geoffrey Sneddon wrote:
> 
> @scheme is defined as "The 'scheme' attribute is an IRI that identifies
> a categorization scheme". Is this therefore like atom:id, in that it is
> an identifier, and the actual IRI is meaningless.
> 
> - Geoffrey Sneddon
> 
> 
>

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From: "A. Pagaltzis" <[email-masked]>
Date: Tue, 1 May 2007 22:05:04 +0200

* Geoffrey Sneddon <[email-masked]> [2007-05-01 20:20]:
> identifies a categorization scheme". Is this therefore like
> atom:id,  in that it is an identifier, and the actual IRI is
> meaningless.

It’s just like `xmlns`.

Regards,
-- 
Aristotle Pagaltzis // <http://plasmasturm.org/>

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From: Geoffrey Sneddon <[email-masked]>
Date: Wed, 2 May 2007 16:41:52 +0100

> The IRI has meaning, it just may not be dereferenceable.

What meaning? According to the spec it's just an identifier, not a  
unique identifier (like atom:id), so it isn't overly useful even  
within the same feed to use as an identifier. If it isn't  
dereferenceable and contain a page about the category, what practical  
use does it have?

- Geoffrey Sneddon

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From: James M Snell <[email-masked]>
Date: Wed, 02 May 2007 11:53:40 -0400

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.

Essentially, the scheme identifies the ontology to which the term belongs.

- James

Geoffrey Sneddon wrote:
> unique identifier (like atom:id), so it isn't overly useful even within
> the same feed to use as an identifier. If it isn't dereferenceable and
> contain a page about the category, what practical use does it have?
> 
> 
> - Geoffrey Sneddon
> 
> 
>

---

From: Geoffrey Sneddon <[email-masked]>
Date: Thu, 3 May 2007 18:14:30 +0100

> "bookmark", "chat", etc) has a very specific meaning in the Lotus

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.

- Geoffrey Sneddon

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From: Sylvain Hellegouarch <[email-masked]>
Date: Thu, 03 May 2007 18:27:04 +0100

Geoffrey Sneddon wrote:
> 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.

It may be worthless to aggregators but a powerful attribute for
applications that are built atop APP. Imagines a CMS that uses APP to
perform its operations, the scheme could denote different meaning within
the context of the CMS.

You could also imagine an automated service that "converses" with an APP
service. This automation could give a specific meaning to the scheme
attribute again.

APP goes way beyond the aggregators-space.

- Sylvain

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From: Bill de hOra <[email-masked]>
Date: Thu, 03 May 2007 19:11:42 +0100

> should probably be left to namespaces where attributes can be defined 

You're conflating "practical use" with "complete unambiguity". Don't 
start from there. Not even languages with actual semantics (KIF, RDF) 
will give you that.

cheers
Bill

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From: Geoffrey Sneddon <[email-masked]>
Date: Thu, 3 May 2007 19:09:30 +0100

On 3 May 2007, at 18:27, Sylvain Hellegouarch wrote:

>> whatsoever,

Surely it would therefore be defined in APP then, not the syndication  
format?

- Geoffrey Sneddon

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From: "Bob Wyman" <[email-masked]>
Date: Wed, 9 May 2007 20:00:44 -0400

On 5/3/07, Geoffrey Sneddon <[email-masked]> 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.
> 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

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From: Eric Scheid <[email-masked]>
Date: Thu, 10 May 2007 17:05:24 +1000

On 10/5/07 10:00 AM, "Bob Wyman" <[email-masked]> wrote:

> [...]

> addition to label and schema.

in XTM and others, the PSI isn't a sole attribute, but instead a given
category could have multiple PSI, and hopefully one or two in common with
the PSIs that you are using in your schema.

As such, is there any reason we can't do something like this:

    <atom:category scheme="..." term="..." label="...">
        <xtm:psi uri="[1]"/>
        <xtm:psi uri="[2]"/>
        <xtm:psi uri="[3]"/>
    </atom:category>

Hmmm ... better yet:

    <atom:category scheme="..." term="..." label="...">
        <atom:link rel="psi" href="[1]"/>
        <atom:link rel="psi" href="[1]"/>
        <atom:link rel="psi" href="[1]"/>
    </atom:category>

(hrmmm again though ... while atom:category allows for undefinedContent as
child elements, the RNG definition of undefinedContent disallows atom:* ...
meaning we can't do the second example above. Bugger. Think anyone will
notice?)

e.

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From: "Bob Wyman" <[email-masked]>
Date: Thu, 10 May 2007 11:03:10 -0400

On 5/10/07, Eric Scheid <[email-masked]> wrote:
> category could have multiple PSI, and hopefully one or two in common
> with the PSIs that you are using in your schema.

Eric is, of course, correct. An arbitrarily large, but hopefully small,
number of subject indicators can be associated with a single entry in an
ontology. In such a case, each of the subject indicators *should* be
considered by the creator of the category element to be semantically
equivelant. Thus, one might find the following:

<atom:category scheme="..bobs_ontology"
                        term="Communication.Publication.Book"
                        label="Book">
  <atom:link rel="psi" href="http://de.wikipedia.org/wiki/Buch"/>
  <atom:link rel="psi" href="http://en.wikipedia.org/wiki/Book"/>
</atom:category>

What that says is that the concept or thing which is categorized as "
Communication.Publication.Book" in bobs_ontology is referred to by humans as
"Book" and is the same thing which is identified by the listed German and
English Wikipedia URIs. If, in some other schema, (such as "Great
Inventions") someone else was to create an entry that linked to either of
the two Published Subject Indicator URIs, we would be able to infer
transitive similarity between the term for a specific "Great Invention" and
the term "Communication.Publication.Book" in bobs_ontology. In this way, of
course, we can support cross-ontology reasoning, translation between
languages, etc.

In a system that doesn't support PSIs or a similar concept, there is really
no way to reason about the meaning of any term unless you have intimate
knowledge of the schema that defines it. One might be able to establish
precise equivelances between terms in a small number of "popular"
ontologies, however, that is a very expensive process which requires a great
deal of communication overhead and continued maintenance as terms are added
or modified. It is better, I think, to let understanding emerge from an
analysis of the encoding of the data -- even though that understanding might
be a bit fuzzy.

bob wyman