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Re: Alternatives to containers/collections (was Re: Requirements for a possible "RDF 2.0")

From: Frank Manola <fmanola@acm.org>
Date: Thu, 14 Jan 2010 16:49:56 -0500
Message-id: <46DE9CF1-B561-4F1A-967F-966ABA30586C@acm.org>
Cc: Semantic Web <semantic-web@w3.org>
To: Pat Hayes <phayes@ihmc.us>

On Jan 14, 2010, at 3:19 PM, Pat Hayes wrote:

> 
> On Jan 14, 2010, at 11:31 AM, Dan Brickley wrote:
> 
>> On Thu, Jan 14, 2010 at 4:20 PM, Pat Hayes <phayes@ihmc.us> wrote:
>>> A lot, perhaps all, of this hair could be avoided if RDF allowed general
>>> tuples as well as triples. All that is needed is some way to put N things
>>> into a sequence: so, put N things into a sequence. The 'graph model' would
>>> be a hyperlink, drawn as a polygon (eg triangle for N=3) rather than a line.
>>> In triples-style syntax, it would just be moving a dot.
>> 
>> I periodically wonder what an RDF without the binary restriction would
>> look like.
> 
> My 2c suggestions, as answers to the questions.
>> 
>> Would each property/relation have a fixed arity, eg. dc:source might
>> 'be a 4', 'foaf:knows' a 7?
> 
> No. But it might be useful to distinguish 'really binary' ones, which only fit in triples, from the others, which can take any number of things in the sequence. Or maybe not, whatever. But the default should be, any number (even though most of them will be 2 in practice, ie triples.)
> 
>> That doesn't make a lot of sense to me. So
>> presumably they'd vary freely. In which case, we have a lot of
>> figuring out to do when wondering whether   livesWith(alice, bob,
>> 2007, 'y') implies livesWith(alice,bob) or livesWith(alice, bob, 'y',
>> 'foo.html'). The binary straightjacket makes some of these questions
>> impossible, albeit maddeningly...
> 
> The Common Logic answer is very puritan: each number of arguments is a separate assertion, and they are all independent (unless you write axioms connecting them.) So liveswith(a b c) has nothing to do with liveswith(a b) or with liveswith(a b c d), etc., as far as the logic itself is concerned.  This is actually quite elegant and works well WHEN you can write the axioms you might need. So maybe we would need, for RDF, some way to attach some common inference patterns to these by giving properties to the property of the tuple. For example, one useful and common pattern allows ends of argument lists to be lopped off, so that
> 
> liveswith(alice, bob, <address>, <maritalstatus>)
> entails
> liveswith(alice, bob)
> 
> and we might specify this pattern (in a semantically extended RDF) by asserting
> 
> liveswith rdf:type rdf:ExtendableProperty .
> 
> But this is very much off the top of my head. Whaddayathink?

Pat--

Could you carry this Common Logic example a bit further?  Suppose we have the tuple

liveswith(alice, bob, "4255 18th Street NW, Washington, DC", "married")

In the relational data model, I might have declared the relation "liveswith" as having columns "wifename", "husbandname", "address", and "maritalstatus", so I know how to interpret the various arguments of the tuple.  But how do I make this association (e.g., between the third argument of the tuple and "address") if I encounter this  tuple "in the wild" of the semantic web?  How does Common Logic deal with this?  This may be a confession of ignorance of something really basic, but this issue, to me, was always one of the reasons for favoring a purely binary approach.  You always knew what the various parts of the triple signified, without having to go off and find some other declaration somewhere.  

--Frank
Received on Thursday, 14 January 2010 21:50:34 UTC

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