[sc34wg3] TM Data Model issue: prop-subj-address-values

Kal Ahmed sc34wg3@isotopicmaps.org
27 Oct 2003 20:33:16 +0000

My opinion is that [subject locator] has to be a single resource if the
concept of a subject-constituting resource is to have any real meaning
in a topic map.

What would it mean for a topic to have two different subject
constituting resource locators ? If the two locators resolve to the same
resource representation (e.g. mirror sites), then they are *not* the
same resource so you have a topic that represents two different subjects
and that is not allowed. If you want to assert that the two resources
provide representations of the same subject, then you should be using
subject indicators.

More tricky is the case where two locators return the same resource (e.g
because of server-side settings that turn http://www.techquila.com/ into
http://www.techquila.com/index.html), but in a heuristic (which is what
this is), you have to sometimes accept that you need to be inexact to
produce something workable.

If you were to allow multiple subject locators, you would not only allow
the arguably correct case of two locators which return the same
resource, but also a whole raft of incorrect cases where the two
locators return different resources. [subject locator] is the lesser of
these two evils.=20



On Thu, 2003-10-23 at 15:02, Geir Ove Gr=C3=B8nmo wrote:
> I have a comment on the latest TMDM commitee draft dated 2003-10-22.
> The [subject addresses] property on the topic item has been renamed to
> [subject locator]. I agree with the name change, but I'm rather
> sceptical of it no longer being a collection property. A consequence is
> the following constraint:
> """
> Constraint: Subject locator collision
>    Two topics being merged cannot have different values in their
>   [subject locator] properties.
> """
> This constraint prohibits automated merging of topic maps in the cases
> where two topics are bound to be merged based on identity, e.g. when
> they have subject indicators in common, but the two have different
> subject locators.
> It looks to me that only a human being can resolve such an issue. This
> is extremely unfortunate and inconvenient. The two topics have after all
> been considered to be the same topic because of their other identities.
> If a topic had more than one subject locator the subject locators
> should of course all reference the _same_ information resource. In my
> opinion it is only a problem when it can be _proved_ that they are not
> the same information resource. There could be many reasons why an
> information resource could have more than one valid locator.
> What was the rationale for the change in the draft?
> Geir O.
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Kal Ahmed <kal@techquila.com>