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Re: Semantic Web permathread, iteration n+1 (was Re:


expressiveness and tractability
Elliotte Rusty Harold wrote:

> At 9:56 PM -0400 6/4/04, Thomas B. Passin wrote:
>
>> Right, an arbitrary piece of xml does not carry enough information to 
>> let you automatically distinguish between elements that represent 
>> things and those that represent properties.  A person generally has 
>> to work that out.  But when you do have a properly striped format, it 
>> can be easy to turn into rdf (it's usually just about there as is).
>
>
>
> Why is there a distinction between "things" and "properties"? Isn't a 
> property a thing? Can't a property have properties of its own?


I'll jump in so I'm not letting my favourite permathread go without 
acknowledgement...

A benefit of having descriptive statements in RDF is so that you can use 
query and inference on them. You'll want to know that you can get 
solutions, and get them in reasonable time. The logic (specifically 
Description Logics) is reasonably well worked out around RDF/OWL, and 
apparently the tractability goes out of the window as soon as you get 
into fancy stuff with properties. A logician could probably be more 
specific in their description of fancy stuff.
Essentially it's a trade-off between expressiveness and tractability.

Cheers,
Danny.

-- 

Raw
http://dannyayers.com


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