[sc34wg3] Issue merge-srcloc-vs-subjid

[Lars Marius Garshol]

* Jan Algermissen
| 
| I don't really know what a source locator is, but I assume it is the
| URL of the <topic> element, yes?

Provided the topic was created from reading in a <topic> element that
is correct. You can also assign source locators by other means, but
this is the default use of them.
 
| Then (assuming map.xtm as the base URI for the map )
| 
| <topic id="t1" />
| 
| is the source (source element?) for a topic and the
| topic will have the source locator map.xtm#t1, yes?

Correct.
 
| In addition to the source locator, a topic can have a set
| of subject indicators and both can be used to refer to that
| topic equally, yes?

Also correct.
 
| The approach that PM4TM [1] and the early RM [2] take is to make the
| node demander locator a subject indicator too.

I know. We discussed this at length at several SC34 meetings and so
far there has been agreement that source locators and subject
identifiers need to be distinct. When you serialize a SAM instance to
XTM you do not want to find <subjectIndicatorRef> references to all
the source <topic> elements in that XTM. 

Therefore the model needs to maintain a distinction between true
subject indicators and source elements so that it can do the
reserialization correctly.

What this issue is about is what to do when a locator appears in both
roles: it's both used as a subject identifier *and* as a source locator. 
 
| I am not sure if this is of any help, but maybe...
 
Well, essentially what you've done is to point out that I left out one
possible resolution from my list of proposed resolutions: to merge
the notions of source locators and subject identifiers. It *is* a
possible choice, but would entail being unable to distinguish between
references to <topic> elements and references to true subject
indicators. 

It would also mean that most XTM exports would contain at least one
junk <subjectIndicatorRef> for every <topic> element and that repeated
roundtripping would cause the set of junk references to grow with each
roundtrip. 

Admittedly it is less elegant than it could be to have three kinds of
URIs for topics, it's just that I can't see any cure for this disease
that is less harmful than the disease itself.

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