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Re: bnodes as answer bindings

From: Pat Hayes <phayes@ihmc.us>
Date: Sun, 6 Aug 2006 20:58:02 -0700
Message-Id: <p06230912c0fc6495e5d5@[192.168.1.6]>
To: Bijan Parsia <bparsia@cs.man.ac.uk>
Cc: RDF Data Access Working Group <public-rdf-dawg@w3.org>

>On Aug 4, 2006, at 11:11 PM, Enrico Franconi wrote:
>
>>
>>>Can you give references for all this 
>>>terminology that you cite? What exactly is the 
>>>"active" domain? There is nothing in any 
>>>semantic theory that I know of that 
>>>distinguishes *things in the domain* on the 
>>>basis of the kind of name that is used to 
>>>refer to them with. The idea does not make 
>>>sense, in any case: if bnodes were obliged to 
>>>refer to a non-active domain while names refer 
>>>to something else, then the troublesome 
>>>redundancies would be eliminated.
>>
>>The first entry in 
>><http://scholar.google.com/scholar?q=%22active+domain%22+database> 
>>is a survey in DBs written 20 years ago.

OK, thanks for that. I can't actually get the 
article on-line from this, and the abstract does 
not use 'distinguished' or 'active' anywhere. But 
I will continue to search.

>>>I have never previously heard of this 
>>>terminology of "distinguished" vs. 
>>>"nondistinguished". (You have everyone's 
>>>permission at this point to roll your eyes in 
>>>amusement at my profound ignorance, of 
>>>course.) I would be interested to see where 
>>>this terminology was first used, and what its 
>>>history is. In a database context where there 
>>>are no bnodes, the distinction would be 
>>>vacuous.
>>
>>Ah. Second and third entries in 
>><http://scholar.google.com/scholar?q=distinguished%20variables> 
>>are DB references from almost 30 years ago.

Thanks again. Similar access problems.

>And Pat's own acquaintance with some variants of the latter terminology:
>	http://daml.semanticweb.org/listarchive/joint-committee/1024.html
>	http://pride.daml.org/listarchive/joint-committee/1125.html
>
>and
>	http://daml.semanticweb.org/listarchive/joint-committee/1027.html

Indeed, I had forgotten that we did use this 
terminology at one point in DQL; but we used it 
with a completely different meaning, which had 
nothing to do with what the variable is allowed 
to bind to. (In retrospect, a better term for the 
DQL notion would have been 'selected variable': 
it meant only a variable whose binding is 
returned in an answer.)  I note that in the 
DATALOG literature the term is used with yet a 
third meaning, viz. a variable which occurs in 
the head.

Not surprisingly, the phrase "distinguished 
variable" seems to be used for a variety of cases 
in which someone wishes to distinguish one 
variable from another. This however does not make 
it a widely used technical term, only a common 
English phrase. Apparently, in fact, these 
various uses - and I am sure one could easily 
find others - have very little, if anything, in 
common.

>I believe the most deeply nested quote is 
>Richard Fikes, the next level Pat, and the final 
>line richard (in spite of the quote mark):
>
>"""> >answer will include a binding for each distinguished variable.  
>I am
>>  >referring to the variables in the query pattern that are not
>>  >distinguished variables as "non-distinguished variables".
>>
>>  undistinguished variables?
>
>>From a quick check on the Web, I find them being called
>"nondistinguished variables"."""
>
>I don't expect Pat to have remembered this. It 
>was, after all, 5 years ago. It seems there is 
>precedent for semi-distinguished variables in 
>DQL.

This terminology of 'semi-distinguished' is 
silly. These are simply *variables*, plain 
vanilla. A variable is a syntactic token whose 
role is to stand in for, or be replaced by, or be 
bound to, a piece of syntax so that the resulting 
expression is well-formed. This notion of 
variable is used a wide variety of contexts and 
has been so used for at least 50 years (lambda 
calculus, substitutional interpretation of 
quantifiers, production rules): there is nothing 
new or exotic about it. Both 'distinguished' and 
'undistinguished' variables, in the sense you are 
using these qualifiers, are variables which are 
restricted in some way to bind only to a certain 
class of syntactic instances. But to call an 
variable without any such restrictions applied to 
it 'semi' anything, and to claim it is something 
new, is daft. These are just plain *variables*, 
and this idea is about as old as algebra.

BTW, in the DQL sense of 'distinguished', 
"semi-distinguished" would be incoherent. (Do you 
return half the answer?)

Pat

>Richard Fikes seems (without having examined all 
>the email) to have been the driver.
>
>DQL reference is the third hit:
> 
>	http://www.google.com/search?hl=en&lr=&client=safari&rls=en&q=distinguished+variable&btnG=Search
>
>Cheers,
>Bijan.


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Received on Monday, 7 August 2006 03:58:24 GMT

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