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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
transformation 
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
DAML?)
[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 

hth

Steve

[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 GMT

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