Kudos to Dave for pulling up his socks and discovering what Semantic Web technologies have to offer first hand – you know, all that wonderful extensible goodness I’ve been going on about after discovering it for myself.
He talks about a perceived problem here …
In order to prevent an area code, I need to add the area code with a cardinality of 0. Now I think this is a pretty big problem. The whole Semantic Web world view of open content models comes and bites us here. The rough assumption is that if a property isn’t specifically exluded, it might be related to the thing.
That’s not quite right. It’s one thing to look at the information space that is the Web/Sem-Web and see two separate but related resources (e.g. the PO and the customer), but it’s something else entirely to look at a message on the Web and conclude that there might be some data elsewhere which is intended to be communicated. That’s where self-description comes in, and it prescribes that if a message arrives with a PO and without a customer, then the customer information is not part of the message, as you require. What Bijan seems to be talking about is the former, not the latter, i.e. to avoid closed world assumptions.
He adds;
If we think of the main point of a schema language as defining the language for exchanging information, it seems that RDF/OWL is a easier to use for extensibility and versioning. Which might be no surprise given the design centres. But given the inability to control the schemas in all the right facets – such as mandatory extensions – it doesn’t fully solve the problems of large scale distributed system extensibility and versioning. More work to be done….
…which is true, I think there is more work to be done (though I also think what’s done is a decent 80-90% solution, just as HTTP is despite not having mandatory extensions). More on mandatory extensions and RDF later though; I’ve given this subject a lot of thought (and code) over the past couple of years.
P.S. I think it’s really interesting that Web services proponents are discovering the virtues of the Semantic Web before they really appreciate all the Web itself has to offer. I totally didn’t see that coming! Coincidentally, check out this message (lists.w3.org is having issues right now, stay tuned…) where an OWL-S user realizes some of the problems with the Web services model.
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