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Re: [Graphs] g-text equivalence

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 19 Mar 2011 20:29:31 -0500
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, RDF Working Group <public-rdf-wg@w3.org>
Message-Id: <E1674B1C-8F59-4EB5-8806-C9584D70A8FC@ihmc.us>
To: Sandro Hawke <sandro@w3.org>

On Mar 19, 2011, at 7:16 PM, Sandro Hawke wrote:

> On Sat, 2011-03-19 at 19:02 -0500, Pat Hayes wrote:
>> On Mar 18, 2011, at 3:56 PM, Sandro Hawke wrote:
>> 
>>> On Fri, 2011-03-18 at 19:22 +0000, Andy Seaborne wrote:
>>>> 
>>>> Is g-snap->g-text is just a function of the content type?
>>> 
>>> Well, probably, for our purposes, I think so.  
>>> 
>>> There's a trivial case where it's not: the  arbitrary non-semantic
>>> variability in serialization, eg whitespace.  So, some notion of
>>> equivalence class of g-texts may be important.
>> 
>> Can't we simply *define* g-texts to be equivalent under such trivial variations? It is our notion, after all.
> 
> I'm not quite sure what you mean.  I think it's important the g-text be
> a subclass of character or byte strings, so *equality* is string
> equality.

Well, that kills my suggestion right there. So let me push back on this point. Why do you think this is important? Why should a g-text not have its own g-style notion of equality? Why should it be a subclass of byte strings? 

>  For equivalence, yes, it seems like there's a simple and
> obvious meaning of equivalence, but I don't know how to formalize it,

You did later in the message :-)

I guess my overall question is, why do we need to distinguish identity from equivalence? Maybe this question is a residue from when I used to think like a mathematician, but I'd be interested in your answer.

Pat

> and I maybe it's not that quite that simple, for example:
> 
> g-text t1: '_:x <http://www.w3.org/2000/01/rdf-schema#comment> "Hello"'
> g-text t2: '_:x  <http://www.w3.org/2000/01/rdf-schema#comment> "Hello"'
> g-text t3: '_:y <http://www.w3.org/2000/01/rdf-schema#comment> "Hello"'
> 
> I think all of the are equivalent, but the equivalence of t1 and t2
> (where the difference is just whitespace), seems somewhat different from
> that between either of them and t3 (where the difference is in blank
> node labeling).
> 
> Should we just define a single standard "equivalence" of g-texts, or do
> we need to allow room for there being several different kinds?

Why would anyone need different kinds?

> 
> Maybe the simple notion is "semantic equivalence" of g-texts, which I
> might define as:   T1 and T2 are semantically equivalent iff the RDF
> graphs produced by correct parsing of either of them are
> indistinguishable.   
> 
>   -- Sandro
> 
>> Pat
>> 
>>> 
>>> There's a related problem I don't know if we can or should address,
>>> which is how to deal with websites which use cookies or other
>>> information (IP address, browser sniffing, etc) to customize content.
>>> 
>>> Does AWWW deal with these at all?   Not that I recall.
>>> 
>>> For an RDF example, I could make it so http://hawke.org/ip returns
>>> something like 
>>> 
>>>       { <> eg;currentClientIP "128.113.1.1" }
>>> 
>>> ... but returning your actual IP address.  Given the right cloudhosting
>>> infrastructure, I could meaningfully, and perhaps usefully, return two
>>> different non-equivalent g-texts (ie g-texts for different g-snaps), at
>>> the exactly same moment in time.
>>> 
>>> So, I think the model of web addresses identifying g-box which contains
>>> one g-snap at any point in time is as good as REST, and probably good
>>> enough, but still not perfect.
>>> 
>>>   -- Sandro
>>> 
>>> 
>>> 
>>> 
>> 
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>> 
>> 
>> 
>> 
>> 
>> 
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Sunday, 20 March 2011 01:30:07 UTC

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