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RE: relational mapping?

From: Cayzer, Steve <Steve_Cayzer@hplb.hpl.hp.com>
Date: Fri, 4 May 2001 09:33:26 +0100
Message-ID: <5E13A1874524D411A876006008CD059F01225190@0-mail-1.hpl.hp.com>
To: "'Danny Ayers'" <danny@panlanka.net>
Cc: RDF-Interest <www-rdf-interest@w3.org>
fyi, I came across a paper recently which describes a bijective
from an Entity Relationship model to ERL (a simplified description logic)

The authors' intention was (I think) more to provide data validation above
and beyond what is possible
in a typical RDB schema but it seems to me you could map ERL to RDF (via
[I confess I merely skimmed it but it looks like it could be useful to you]

Author Hacid, M.-S.,Petit, J.-M.,Tourmani, F. 
Journal Knowledge and Information Systems 
Volume vol.3, no.1 
Abstract We address the problem of reasoning about database conceptual
schemas by exploiting the possibility of using a description logic. We
develop an approach by using as a foundation an entity-relationship model
that displays features such as ISA, disjointness and cardinality
constraints. We propose an equivalence-preserving transformation of entity
relationship schemas into terminologies in a description logic. This
equivalence, based on the measure of information capacity, ensures that the
semantics of entity-relationship schemas is accurately captured by the
corresponding terminologies. As a consequence, reasoning on
entity-relationship schemas is appropriately reduced to reasoning on
terminologies in a description logic 
InclusivePages 52-80 
CorporateSource LISI, Villeurbanne, France 
Publisher Springer-Verlag 
DateOfPublication Feb. 2001 



[btw, I am not cross-posting this to cut down on RDF Logic traffic. But if
any logicians are reading this it would be 
interesting to see what they make of ERL]

Steve Cayzer    HP Labs, Bristol, UK    mailto:Steve_Cayzer@hp.com

-----Original Message-----
From: Danny Ayers [mailto:danny@panlanka.net]
Sent: 03 May 2001 17:59
To: Jan Grant
Cc: Www-Rdf-Logic; RDF-Interest
Subject: RE: relational mapping?

<- I've done quite a bit of thinking about it; got some paper notes which
<- I'm in the (slow) process of typing up. You're right, there's a simple
<- mechanical mapping of rows in a table to RDF; what you lose by this is
<- the natural linking of properties.

Not sure I understand - linking of properties in the RDF?

<- For a sufficiently normalised relational schema*, you can generally
<- produce a mapping
<- 	(primary key) -> resource
<- 	(other values) -> properties
<- 	(foreign key) -> link to resource representing primary key for
<- 			foreign table

Great - this looks very promising, just the kind of thing I was looking for,
I'm going to have to get pencil & paper.

<- * that is, very (what, fifth NF?): for instance, moving one-to-one data
<- into a separate table if the data describes a separate concept; it's
<- generally possible to produce a normalised schema from a less normalised
<- (ie, more real-world) one with the judicious use of views.

Ugh! I've been postponing re-reading on the later NFs, hoping I wouldn't
have to. Rats.

I foolishly didn't say what I was wanting to do with the mapping - off list
I've been mailed some good links for going RDF -> RDBMS (thanks!), but I'm
really looking at RDBMS -> RDF and (as you seem to have mind-read) was
wondering whether there was a way up from relational <-> RDF model.

The plan is to expose a RDBMS, starting with metadata, trying to preserve as
much of the logical structure as possible. I'm currently thinking this way :
pump out the top-level information as RDF, linked down to a dynamically
generated XML Schema that will pass on the constraints for any actual data
requested, which will in turn be presented as straight XML. I reckon if I
can get the RDF right, the rest should follow mechanically. Hopefully ;-)

I was considering doing the mapping within the DB, generating a table of
triple using the logical capabilities of the RDBMS. This is very appealing
from the point of view of integrity (& probably efficiency), but the stuff
will still need to be poured out in a form that other systems will
understand, and application-level constraints will almost certainly be
needed at the other end anyway, so it's code-hacking time whatever happens.

Thanks for the info. Now where's that pencil...
Received on Friday, 4 May 2001 04:34:01 UTC

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