Sean and others,
First, the success in mapping from an EXPRESS schema to an OWL ontology
depends on the style in which the EXPRESS schema was written. OWL
itself has many uses and styles, so nothing new about that. The reeper
tool, of which I am the author, has an initial EXPRESS to OWL mapping
that is a 'structural mapping' largely aimed at enabling exchange of
data using RDF as a data encoding rather than Part 21 - what some call
a proxy ontology of the EXPRESS, rather than a rich ontology of the
domain of discourse. So, while I agree it has little value on the
Semantic Web to do not agree it's not a sensible thing to do. I'm
looking at a PLCS-based project where it enables a far superior
technical solution to data exchange because of its tight integration
with PLCS Reference Data which is modeled as OWL taxonomies.
It's my contention is that there is no general EXPRESS to OWL mapping
possible if the requirement is to produce a semantically-useful
ontology. You must have knowledge of the meaning of the entity types in
the EXPRESS schema in order to produce useful OWL. Based on that
knowledge, a human would configure the mapping based on individual
entity types or common patterns in the schema and the tool could
produce useful OWL. So, my longer term aim for reeper was to create a
configurable
mapping from EXPRESS to OWL to address the issues you and others have
raised. The supported pre-built configurations were to be based on
patterns of EXPRESS usage.
Base to the SC4/STEP question - I imagine what whoever made the
statement meant was that for SC4 usage, there are very few cases where
OWL could not replace EXPRESS as the base modeling language for the
standards. That's certainly something I believe. In cases where OWL
doesn't do everything EXPRESS does, other approaches can supplement the
OWL (e.g. a lack of OWL support for cardinality can be handled by an
XML Schema derived from the OWL for the purpose of data exchange). By
the way, translating EXPRESS to UML first doesn't solve everything - it
turns out that UML doesn't support the full set of INVERSE capabilities
EXPRESS has.
Cheers,
David
On 17/10/10 20:13, sean barker wrote:
John,
Thank you for your answer on the relative expressive powers of OWL and EXPRESS.
Matthew, Ian
I was not actually proposing to write EXPRESS in OWL, although I believe there is a tool by the name of Reeper that does the translation for you, but I would agree it's not a sensible thing to do.
The point was rather that, if in the semantic web, one came across something that said it was a AP214:Part which was a subtype of a STEP:Product which is a subtype of EXPRESS:Entity, which is a subtype of OLW:thing, would current approaches to the semantic web interpret it correctly? The reason for asking this question is that, in my experience, let a computer programmer loose with some constuct which is intended to have a conventional interpretation and they will ignore the convention, and manipulated according to its computational properties. My understanding is that "semantics" in "semantic web" is concerned with the semantics of the logical operators, rather than the semantics of the terms, such as instantiate from OWL:thing. Hence, if one were to interpret OWL:thing as simply the modelling construct EXPRESS:Entity, would subsequent subtyping to STEPProduct or STEP:Version make further interpetation impossible? Or would this provide another form of Upper Ontology?
Sean Barker, Bristol
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