W3C home > Mailing lists > Public > public-rif-wg@w3.org > July 2007

Application-specific data model options

From: Dave Reynolds <der@hplb.hpl.hp.com>
Date: Wed, 25 Jul 2007 18:42:00 +0100
Message-ID: <46A78B68.4090806@hplb.hpl.hp.com>
To: RIF <public-rif-wg@w3.org>

As I put in a separate email in updating the Arch/DataSets page I put in 
a placeholder section on the question of how how RIF rulesets actually 
make use of application-specific data models.

My attempted summary (which may or may not overlap with Christian's 
action) was:

"""
We have several possible approaches to this question under discussion at 
the moment. These include:

    1.  Library of translators. For a given category of data model we 
define a transformation which will convert that data to a RIF native 
format. The rules are written to manipulate that RIF native form. In the 
case of RDF we have proposed a translation algorithm which would apply 
to any RDF (and thus RDFS or OWL) document, irrespective of the 
associated ontology. For some data models such as XML then the 
translation may be driven by a schema document. RIF itself would define 
only a small number of such translators (perhaps just RDF (schemaless) 
and XML (driven by XML Schema)). Other groups could define additional 
translators and record that fact in metadata but there would be no 
automatic way for an existing RIF implementation to discover and use 
such extension translators.

    2.  Abstract datatypes. In this approach rather than translate data 
into RIF facts, the data is exposed as concrete data types and data is 
manipulated via a set of model-specific builtin predicates and 
functions. In the case of RDF we would have types like graph, triple, 
node and associated predicates including SPARQL queries; in the case of 
XML would have types like Element, Document and associated predicates 
such as XPath-like navigation.

    3.  Single meta translator. In this approach RIF adopts a single 
meta-meta modeling language (perhaps MOF or KM3)and defines a single 
transformation algorithm. For any data model category we define a 
meta-model for it, expressed in our standard meta-meta modeling 
language. The transformation algorithm can translate any instance data 
for which there is an associated model and meta-model to RIF native 
format. RIF would only define a small number of such meta-models but the 
external groups could adopt additional ones. In this case the associated 
meta-model could be referenced in the ruleset metadata and a RIF 
implementation could apply the meta-translator without further modification.
"""

I didn't feel it appropriate to put personal commentary on the Wiki 
page, email seems better for that. So here it is.

In some ways I rather like what Hassan was proposing which I've 
attempted to capture in option 3 "meta translator". This seems to give 
greater extensibility and is intellectually more satisfying.

My primary concern is that the resulting mappings may not look very 
intuitive or easy to work with for a specific data model - a 
hand-crafted transformation can be simpler. We also increase our 
coordination problems by having to fit in with other meta-modelling efforts.

Taking RDF/RDFS as a specific test case then I imagine we would 
consider using ODM [*], justifying why W3C was investing in another 
meta-model for RDFS would take some doing. Whilst ODM is a great piece 
of work it is complex, and doesn't model RDFS in the most natural way 
from the point of view of RDF rules languages. I would find the simple 
triple level mapping already proposed rather easier to work with than a 
mapping auto-derived from ODM.

Dave

[*] Ontology Definition Metamodel, not to be confused with ODMG.
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Received on Wednesday, 25 July 2007 17:42:26 GMT

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