Re: Another round of subject identity crisis c.2011

Hi Andrew,

[...]
> understanding of the difference in most cases between subject
> indicators and subject locators (seemingly "old terminology"
> though),
[...]

The term "subject indicator" still exists. The subject indicator is
the resource while the subject identifier is an IRI which refers to
the subject indicator: A PSI is a published subject *indicator*, the
reference to PSI by a topic is a subject identifier.

> I must say I was slightly confused to see that the general
> consensus is that PSI references  seem to only be used as subject
> indic^H^H^H^Hdentifiers and never as subject locators.

PSIs can be used as subject locators but that implies that you make
statements about the resource and not about subject the indicator was
published for. I use this distinction for the PSI template [1] (usage:
[2]). The resource is a topic map (TM/XML encoded) and the IRI of the
resource is used as subject locator to assign statements like author,
created at, modified at, status etc. If you're not familiar with
TM/XML, here a short translation to CTM (prefixes and template
definitions omitted):

     http://psi.example.org/thing
         - "Thing";
         dc:description: "bla bla"
     .

     = http://psi.example.org/thing
         created-by(Joe-Doe);
         status(psi:experimental);
         created-at(2011-03-09);
         modified-at(2011-03-09);
     .

The subject locator is used to attach metadata to the PSI.

[...]
>         mytype = http://psi.myco.com/v1/mytype .

> What have I done?

You've assigned a subject locator to your local identifier "mytype".
That's all. :)

> In my view, what I've done is pulled in the type definition defined
> externally into the local map so that the semantics intended by the
> published topic instance that declares the type 'mytype' don't have
> to be repeated while at the same time explicitly indicating that the
> ontology of the current map is tied to the external resource defined
> by the subject locator.

No, nothing is pulled into your topic map. Your topic map knows
nothing about the ontology at <http://psi.myco.com/v1/mytype>. You
wouldn't pull the HTML into into your topic map if you refer to
http://www.example.org/blog-post.html. You simply state that you'll
make statements about the referenced resource.


[...]
> What are the pitfalls of using a subject locator IF:

> 1) I've made every effort to define the resource in a
> machine-friendly format processable by topic map implementations, and

> 2) I've made every effort to ensure that said resource is served in
> a way that would provide all possible meta-data to indicate that
> this resource WAS a valid topic maps construct rather than any
> arbitrary, untyped resource which could be retrieved from that location.

I'd think that should be application-specific and not solved at the
Topic Maps level. Although I wouldn't use the IRIs of the PSIs at the
application-level for subject locators but I'd try to issue a GET
request to resource in the hope that I get more information about the
subject represented by the *indicator* (i.e. the name and the
description and maybe LOD-alike links to other PSIs). The chance that
you get more information about a resource which was meant to be
consumed by RDF/Topic Maps applications is bigger than trying to
resolve a subject locator and hope that it isn't a bloody HTML page
but something more useful (RDFa may change that, though).

[...]
> BTW, has this always been a google group?  I think this is the
> first time I've ever seen an archived post show up there.

No, it's a mirror created by Benjamin Bock. The official archive is at
<http://www.infoloom.com/pipermail/topicmapmail/>.

[1] <https://code.google.com/p/mappify/downloads/list>
[2] <http://psi.semagia.com/iso8601/2011-03-09>

Best regards,
Lars
-- 
Semagia 
<http://www.semagia.com>

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