>Thanks for the answer. Yes it is quite quite intresting to open the
>discussion on the two issues.
>My understanding is that only if you have in mind the whole picture of
>the RDF/S specifications you may arrive to useful design choices.

That is likely to be true, but surely that is to be expected of most 

>Furthermore, up to know most of the choices are based on the open
>world assumption. However, I din't see any useful reasoning service
>defined on top.

There are several RDF(S) and OWL reasoners available. Details of some 
of them can be found from the relevant W3C websites, or by tracing 
links from the DAML or OIL  websites.

>On the contrary I have seen a lost of useful services
>(validation, efficient storage, query optimization) based on the
>"closed world assuption".

I am not sure how the closed world assumption would provide for 
efficient storage, but you may be right that validation could depend 
on it. However, one should not assume that RDF is *incompatible* with 
a closed world assumption. RDF reasoning is not itself based on a 
closed world assumption because there is no way to 'close' the world 
of a web reasoner, in general. But if a particular application or 
community knows that it can rely on a closed world assumption, and 
has some way to know what the boundaries of that closed world are 
(such as the information in certain set of databases, say) then one 
could make RDF reasoners which rely on that assumption or shared 
knowledge. They would make inferences which are not strictly 
RDF-valid, but that is likely to be common. OWL reasoners, for 
example, make RDF inferences which are not strictly RDF-valid. A 
closed world assumption could thus be considered to be a semantic 
extension to RDF. Open-world reasoning is valid in a closed world; 
the open world assumption is basically just another term for 
logically valid reasoning, and closed-world assumptions represent 
extra assumptions in addition to general logical validity.

>It is quite disappointing that after 4 years of passionate discussions
>on the open world assuption the only real systems that someone can use
>and implement bits of the Semantic Web are based on the "closed world
>assuption". This is quite scary!!!

It might be scary if it were true, but it is not true.

Pat Hayes

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Received on Thursday, 3 April 2003 18:11:52 UTC