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Re: [DTB/Abridged syntax] ISSUE on -equals and -not-equals predicates?

From: Axel Polleres <axel.polleres@deri.org>
Date: Fri, 05 Dec 2008 09:30:43 +0000
Message-ID: <4938F4C3.3090404@deri.org>
To: Chris Welty <cawelty@gmail.com>
CC: Jos de Bruijn <debruijn@inf.unibz.it>, "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>


 >> Probably we need to get rid of the text about "varying between
 >> interpretations". Also, one should add that the truth value of
 >> predicates whose arguments are outside the domain of the external
 >> relation is unspecified.

That is already said in Section 3, item 5...

 >> I think the text should be clear then.


... so, would the following change from

"This means that if one or more of the arguments is not in its intended 
domain, the value of I_external(\sigma)(a1 ... an) can vary from one 
semantic structure to another."

to

"This means that if one or more of the arguments is not in its intended 
domain, the value of I_external(\sigma)(a1 ... an) is unspecified. That 
means in particular, it can vary from one *implementation* to another."

be acceptable in Section 3, item 5.?
As well as changing henceforth in all function and predicate 
descriptions the recurring sentence

"the value [...] is left unspecified and can vary from one semantic 
structure to another. "

to

"the value [...] is left unspecified."


I think that does it.

Axel

Chris Welty wrote:
> 
> 
> -Chris (sent from my iPhone)
> 
> On Dec 4, 2008, at 4:08 PM, Jos de Bruijn <debruijn@inf.unibz.it> wrote:
> 
>>
>>
>> Axel Polleres wrote:
>>> Jos de Bruijn wrote:
>>>>
>>>> Axel Polleres wrote:
>>>>> Jos de Bruijn wrote:
>>>>>> Axel Polleres wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I introduced, as for the other datatypes (along with an editors 
>>>>>>> note),
>>>>>>> -equals and -not-equals predicates for the rdf:XMLLiteral datatype.
>>>>>>>
>>>>>>> There is an obvious overlap between the -equals predicates and '=',
>>>>>>> i.e.
>>>>>>> the '=' built-ins are superfluous, it seems, for dialects that 
>>>>>>> support
>>>>>>> equality.
>>>>>>>
>>>>>>> That is not the case for the not-equals predicates, though:
>>>>>>>
>>>>>>> All the -not-equals predicates, i.e.  pred:numeric-not-equal,
>>>>>>> pred:string-not-equal, pred:dateTime-not-equal, pred:date-not-equal,
>>>>>>> pred:time-not-equal, pred:duration-not-equal,
>>>>>>> pred:XMLLiteral-not-equal,
>>>>>>> pred:text-not-equal
>>>>>>>
>>>>>>> are defined on the same domains as their positive counterpart with
>>>>>>> reversed truth-values.
>>>>>>>
>>>>>>> That has the consequence though, that they are not possibly
>>>>>>> emulated by
>>>>>>> negation as failure, i.e. it is in general not true to say that the
>>>>>>>
>>>>>>> -not-equals version is true, whenever the -equals version is NOT 
>>>>>>> true.
>>>>>>>
>>>>>>>
>>>>>>> An example:
>>>>>>>
>>>>>>> _a:-  External (pred:numberic-equals("blabla", 1) )
>>>>>>> _b:-  External (pred:numberic-not-equals("blabla", 1) )
>>>>>>>
>>>>>>> entails neither _a nor _b, however
>>>>>> Both rules contain errors, and since errors mean arbitrary truth
>>>>>> values,
>>>>>> you don't know whether _a or _b are entailed, and in practice I 
>>>>>> suspect
>>>>>> applications will terminate with some error message.
>>>>> No, that is not what the semantics says... it says that the 
>>>>> truth-value
>>>>> may vary from interpretation to interpretation and that means it is 
>>>>> not
>>>>> true in all interprestations which means it is not entailed.
>>>>
>>>> No. We leave it up to the user, which means the user can choose to make
>>>> it true in every interpretation.
> 
> This was my understanding. ( I think I proposed it) but I agree the 
> following could be understood as saying something else:
> 
>>>>
>>>
>>> I assume that this is your reading of
>>>
>>> "If the argument value is outside of the intended domain or outside the
>>> partial conversions defined in [XPath-Functions], the value of the
>>> function is left unspecified and can vary from one semantic structure to
>>> another."
>>>
>>> interesting opinion.
>>
>> It is what we agreed upon at F2Fx (I believe in Paris).
>>
> 
>>> my reading does not imply what you say. Maybe this
>>> needs clarification then?
>>
>> Probably we need to get rid of the text about "varying between
>> interpretations". Also, one should add that the truth value of
>> predicates whose arguments are outside the domain of the external
>> relation is unspecified.
>> I think the text should be clear then.
>>
> 
> Agreed.
> 
>>
>> Best, Jos
>>
>>>
>>> Axel
>>>
>>>
>>>> Best, Jos
>>>>
>>>>> We do not have errors in RIF, that was decided long ago.
>>>>>
>>>>>>> _a:-  "blabla" = 1
>>>>>>> _b:-  naf ( "blabla" = 1 )
>>>>>>>
>>>>>>> would entail _b.
>>>>>>>
>>>>>>> So, 2 questions:
>>>>>>>
>>>>>>> 1) Do we want this behavior or do we want the negation as failure
>>>>>>> behavior of inequality?
>>>>>> We want this behavior, since this is the only reasonable way
>>>>>> to define these built-in predicates.
>>>>>>
>>>>>>> 2) Do we want the redundancy of equals predicates?
>>>>>> Yes, for dialects that do not supported equality.
>>>>> Same opinion here in both points...
>>>>>
>>>>>> Best, Jos
>>>>>>
>>>>>>> I think we need these things clarified, to be able to determine how
>>>>>>> '=' and "!=" shortcuts in an abridged syntax should be defined.
>>>>> ... which means that '!=' in an abridged syntax would be defined as:
>>>>>
>>>>> numeric-not-equal or string-not-equal or text-not-equal or
>>>>> date-time-not-equal or date-not-equal or time-not-equal or
>>>>> duration-not-equal or XMLLiteral-not-equal
>>>>>
>>>>> and '=' would be defined as equality in dialects that support it and
>>>>>
>>>>> numeric-equal or string-equal or text-equal or date-time-equal or
>>>>> date-equal or time-equal or duration-equal or XMLLiteral-equal
>>>>>
>>>>> in others... Would that the agreed reading for = and != in an abridged
>>>>> syntax?
>>>>>
>>>>> Axel
>>>>>
>>>>>>> Axel
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>
>>>>
>>>
>>>
>>
>> -- 
>>                         debruijn@inf.unibz.it
>>
>> Jos de Bruijn,        http://www.debruijn.net/
>> ----------------------------------------------
>> Many would be cowards if they had courage
>> enough.
>>  - Thomas Fuller


-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/
Received on Friday, 5 December 2008 09:31:25 GMT

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