Re: [topicmaps-comment] mapping topic maps on a relation database

[Lars Marius Garshol <larsga@garshol.priv.no>]

* Lars Marius Garshol
|
| Basically you would have to create a new DTD (call it XTM') and then
| transform from XTM to XTM' before storing it. Otherwise performing
| simple queries like "show me all composer born in Italy" is just
| plain hell to compute, since you would have to do things like
| merging, following three different kinds of references etc during
| the query evaluation.

* Murray Altheim
|
| Unless you always stored already-merged topic maps. 

That would do away with the merging problem, but following three
different kinds of references is not much fun either. That's why I
recommended using a simplified XTM (with no <subjectIndicatorRef> or
<resourceRef> elements outside <subjectIdentity>). A simplified
representation like that would be workable.

The question is also: how are you going to do the processing from XTM
to XTM'? It seems pretty tricky to me, unless you use a OO API to
represent your topic map, and if you do you might as well hide all
that ugly XML stuff behind it. At that point XTM' becomes just another
storage mechanism, and definitely not the easiest to query.

| But you're correct, this isn't a simple matter of storing an XML
| document.  But simple queries of an already-merged topic map (such
| as "get all topics whose base name is 'harrier' in the scope of
| 'birds'" can certainly be done.

Sure, but those are really too trivial to be of much interest. A more
realistic query is "show me all composers who have written operas based
on works written by Shakespeare". It's not that complex, but I think
you have to handle things up to that level *easily* to have a solution
that's worth bothering with. (All IMHO, of course.)

| You just need to be sure that the TM engine is hooked into the DB
| correctly when TMs are brought in and merges are requested. [I'm not
| looking forward to this part of my future...]

Yeah, this isn't the easiest part of TMs to implement, exactly. Doing
it efficiently and under memory constraints makes it even harder.

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
ISO SC34/WG3, OASIS GeoLang TC        <URL: http://www.garshol.priv.no >