[Mulgara-dev] Question about: INSERT/SELECT regression bug

[Paul Gearon]

Just an extra comment on something you said a couple of weeks ago...

On Oct 31, 2006, at 12:05 PM, David Moll wrote:
> One of the operations that we do a fair amount in Mulgara/TKS that  
> gives us a bit of a headache is doing modify/deletes.  Mainly  
> because we need to ensure that when deleting a triple, we don't  
> leave any "orphaned" triples lower on the graph.
>
> My end goal is to fully automate the ability to insert, modify and  
> delete information in the data store with a thin client that will  
> automatically generate the proper iTQL queries based on user  
> input.  In building up to this, I am trying to determine exactly  
> what queries I need to run in order to successfully modify  
> information in the data store.

Your comments (and the ensuing question) imply a problem with the  
lack of a "modify" operation.  I agree that this is an issue, but at  
the same time I'd like to defend Mulgara by pointing out that this is  
not an RDF issue.

RDF is all about "statements".  This is what Mulgara works with.   
 From this perspective, Mulgara does it's work just fine.

To think about objects with properties that can be "changed", you are  
applying a new layer of semantics over RDF.  These semantics are  
reasonably well described in RDFS, and even more-so in OWL.  But  
without this level of semantics, the statements of:
   <_:personA> <ns:hasName> "Fred"
and
   <_:personA> <ns:hasName> "Fred Flintstone"
Are completely unrelated statements.  They may share the same subject  
and property, but that's it.  This is the cause of your difficulties.

While RDF is a fantastic building block, I think that it is very  
important to have a semantic layer over the top as well.  A few  
months ago at work I had to build just such a layer, where objects  
with properties were defined, and even some OWL structure was put in  
place.  While doing this I encountered exactly the same problem with  
"updates".  However, this is definitely an issue at the higher  
semantic level, rather than in Mulgara itself.

I'd like to see a semantic API like this released as a library for  
Mulgara, maybe as a new API, or possibly as a sister project.  It  
should certainly make use of the rules engine, with RDFS, and ideally  
with OWL.  It would be nice to release the code I've done already,  
but that belongs to my employer rather than me.  However, I can tell  
you from experience that this approach is very powerful, and makes  
life a lot easier for anyone doing RDF/RDFS/OWL modeling.

Is anyone interested in looking at this with me?

Paul
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