[topicmapmail] DM zero source locators

[Kal Ahmed]

On Sat, 2003-08-16 at 11:37, Peter P. Jones wrote:
> On 15 Aug 2003 at 20:48, Lars Marius Garshol wrote:
> 
> > 
> > * Peter P. Jones
> > | 
> > | W.r.t. the DM, should an information item should ever be allowed to
> > | have zero source locators?
> > 
> > A similar issue was raised by Kal Ahmed at the meeting in Montréal and
> > resolved there: <URL:
> > http://www.ontopia.net/omnigator/models/topic_complete.jsp?tm=tm-stand
> > ards.xtm&id=topic-identity-required >
> I can't get to that at present - the MSBlast virus DoS is just making 
> stuff time out.
> > 
> > The rationale will appear in the meeting report, once it's published,
> > but requiring a value for one of the three [source locators], [subject
> > identifiers], [subject locator] properties means one can rely on the
> > topic to always have some defined identity.
> > 
> > We can't require a source locator, however, since it's entirely
> > possible to write XTM topic maps where topics are created which have
> > no source locator, and allowing this has been the practice ever since
> > XTM came out.
> Ah. In discussion with Kal off-list he implied that the lack of a 
> source locator was equivalent to the information item having no 
> persistent addressability, and I'm more concerned about that than 
> 'some defined identity'.
> 

Yes, I think that these are two separate issues. Also the issue of
source locators is one that concerns more than just topic information
items.

> So I'm concerned precisely with the creation of new information items 
> prior to any act of persistence, or those which arise as a part of 
> deserialisation, whereby I cannot address those items.
> 
> What is the existing practice concerning the creation of topics that 
> point to topics that were created as a result of some 'node-demander' 
> approach, e.g. subjectIndicatorRef in instanceOf? Or can those never 
> be addressed?

> If they can, doesn't persistence then require the 'demanded' topic to 
> be persisted to satisfy its being addressed?
> 

Topics are different - they have multiple identities: the source
locator, the subject indicator and the subject address. AFAIK the
practice when using subjectIndicatorRef in instanceOf is to call into
existence a topic which has the specified URI as a subject indicator,
but not necessarily any source locator. Because you *can* identify
topics through their subject indicators, this is not really a problem
(e.g. in tolog you can use a subject indicator as a query parameter).

Other information items are different - if an occurrence information
item has no source locator, it cannot be addressed. To my mind, the
question is whether the DM should *require* a source locator for all
information items. My feeling is that being permissive is a good thing
in this case - if your system requires an item to be addressable, give
it a source locator, but I would be wary about requiring TM processors
to augment the DM with source locators, not least because such locators
are not required by XTM syntax.

Cheers,

Kal

> > 
> > -- 
> > Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
> > GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no
> > >
> > 
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-- 
Kal Ahmed <kal@techquila.com>
techquila