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RE: Style question

From: Kirkham, Pete (UK) <pete.kirkham@baesystems.com>
Date: Wed, 09 Mar 2005 13:54:37 +0000
To: ben syverson <w3@likn.org>, semantic-web@w3.org
Message-id: <820DBA1A8ECA1D45A557AFD03CF4DEE06E283E@glkms0015>


> Because RDF/XML is enjoying massive deployment thanks to RSS and FOAF.

The same is true of email - it has an even larger deployment in social networks. Why are you not suggesting we use email for metamodelling or domain models?

About half the feeds I read are Atom. Most of my feeds are about knowledge representation, metamodelling and software engineering, and up to now I've not ever bothered to find out how to do view source, the format is that important. As a user of blogs, it only matters that it works, and RSS works well enough for me not to need to know about it. I do need to know enough html to edit my own entries or to edit the template if I want to.

I've never seen FOAF outside of SW geeks; most 'real world' people I know use vCard if anything (if you type 'friend of a friend' into Outlook's help, it comes up with 'how to remove unsafe attachments', but it understands vCard; not that MS is necessarily the best measure of these things adoption, but it gives you a clue). It's not without merit, but doesn't seem to have any adoption at all - I have never seen an FOAF file on someone's web page or blog who wasn't an RDF head (though I can't say I've been looking either, since I can't do anything with the FOAF when I get it, at least using my work authorised email client, so why would I look for it?). Not that I don't sometimes use the FOAF model for identifying authors in XHTML documents, but there it's just an XML format, not using any RDF or metamodelling techniques; the only difference between using RDF/XML encoded FOAF and XMI encoded FOAF in that case is having an extra stylesheet to change rdf:resource attributes into href attributes so they become navigable by existing browsers.

It is also worth noting that both RSS and FOAF are almost always tree based, so is 'cleaner' to serialise to XML than a general graph such as a metamodel or a domain model - a news feed is very much more like a document than it is instance data in a domain model or a metamodel definition.

> And to be clear, XMI is not an encoding for RDF, but UML, is it not?

Strictly it's an encoding of instances of MOF (meta-object facility) classifiers. UML is defined in terms of MOF, and its metamodel and model classifiers extend MOF classifiers to allow instances of UML classifiers and classifiers defined in UML to be encoded in XMI. MOF is a general abstract syntax there is no reason that XMI cannot be used to encode anything for which an abstract syntax can be written; if you assume the abstract syntax of your metamodel, then you can encode the RDF/XML example you had as XMI in that way. There is more dependence on the metamodel constraining the values (such as "brown,green" being a sequence of simple types rather than a string), though most processing applications have to agree that sort of detail anyway, and most presentation applications don't care. Where type info is required to be inline, you can use xsd types, just as in RDF.

> As someone with an interest in the SW and metadata, I didn't even recognize the excerpt you used as being XMI. That says something.

Yes, to me two things:

It looks a lot like the sort of XML that someone conversant with XML would come up with anyway - which to me is an advantage in a standardised XML format. (if I'd included the outer XMI element tags and namespaces you probably would have realised though). No-one would mistake RDF/XML with something that an XML user would come up with.

That someone with an interest in SW and metadata doesn't recognise the formats for the most widely used metamodelling language in industry, and that someone else with an interest in metamodelling tools and enterprise information exchange doesn't care what format his blog feeds are any more that his email is, maybe says something else too - the communities providing solutions that meet the original aims (data exchange, authentication, metamodelling and web application integration) of SW and OWL and the people interested in the sucessful deployments of RDF are somewhat disjoint.


Given that UML does seem to have won in terms of visual notation and code generation tools (at the expense of most of the notations I was working on or with last decade- if you can't beat them, join them), and has quite strong database design and integration, but RDF has a lot to offer in terms of a formal semantic and inference engine implementations, having a profile defining RDF in MOF that allows both the tools and the engines seems advantageous to me, if only since it means not having two lots of people doing the same thing under different banners.


Pete

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Received on Wednesday, 9 March 2005 13:55:12 UTC

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