Role of the Ontology and Expressivity - to discuss on telcon

This week I commented on the role of the ontology [1] where we should
consider that we are mapping to the following:

   - existing domain ontology (FOAF, SIOC, etc)
   - a putative ontology (automatically generating the ontology from the
   schema/DDL)
   - a federated ontology: combining different ontologies


Eric initially manifested the need to talk about the expressivity [2]. If I
understand correctly the issue of the expressivity is being presented as
"DIRECT - Recapulating Relational Structure" [3] and TRANSFORM -
Non-isomorphic transformation [4].

I'm honestly a bit confused with both of these requirements, but this is my
take on them. Eric, please correct me if I'm wrong:

DIRECT: What I understand is that you could essentially automatically
generate RDF triples (a graph) from the relational data. The top image shows
a graph of relational data and the bottom image shows how the previous graph
can be exposed as RDF (a graph) and it is equivalent (isomorphic) to the
relational data graph.

TRANSFORM: In this section you have taken the previous relational data graph
and put it into the graph structure of two different ontologies. You show
that if you compare the relational data graph with the two graph structures
of the two different ontologies, then the graphs are different
(non-isomorphic).

IF I UNDERSTOOD THIS CORRECTLY... then

What I was mentioning initial (putative ontology and domain ontology) is
directly aligned to what Eric is presenting. Essentially, creating a
putative ontology directly from the sql ddl is equivalent to the DIRECT
requirement and mapping the rdb schema to an existing domain ontology is the
TRANSFORM requirement. Therefore, I propose that this needs to be reworded.
Honestly, it is very difficult to understand and I think the semantic web
and database community would both understand that we are talking about
mapping to an ontology.

Sometimes there doesn't exist a domain ontology that I would like to map to,
therefore I will just use the DIRECT approach. This is what I consider
"direct mapping", therefore we are totally aligned in our thoughts. On the
other hand, you do want to map to existing domain ontologies. These mappings
will have a higher level of complexity.

In conclusion, we I propose that we present these requirements as:

The mapping language should be able to expose the relational data as RDF
without considering a domain ontology

The mapping language should be able to express the mapping between the
relational schema and a existing domain ontology

[1] http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2010Apr/0059.html
[2] http://www.w3.org/2001/sw/rdb2rdf/wiki/Draft_of_Use_Cases#Expressivity
[3] http://www.w3.org/2001/sw/rdb2rdf/use-cases/#DIRECT
[4] http://www.w3.org/2001/sw/rdb2rdf/use-cases/#TRANSFORM
Juan Sequeda
+1-575-SEQ-UEDA
www.juansequeda.com