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Re: PROV-ISSUE-311 (clarify-optionals): Clarify optional arguments in DM [prov-dm]

From: Timothy Lebo <lebot@rpi.edu>
Date: Thu, 19 Apr 2012 08:25:13 -0400
Cc: Luc Moreau <L.Moreau@ecs.soton.ac.uk>, Provenance Working Group <public-prov-wg@w3.org>, Stian Soiland-Reyes <soiland-reyes@cs.manchester.ac.uk>
Message-Id: <2F9E4B04-8E8F-44E7-ADC8-A541B6A25838@rpi.edu>
To: James Cheney <jcheney@inf.ed.ac.uk>

On Apr 19, 2012, at 5:00 AM, James Cheney wrote:

> 
> On Apr 19, 2012, at 5:35 AM, Luc Moreau wrote:
> 
>> Hi James,
>> 
> ...
> 
>> I think the confusion may have come from the description of the grammar but Paolo has reworked it.
>> 
>> As far as the reading of - is concerned, I would even say that we have the following cases:
>> - value exists and is known but not expressed (say, because not deemed important)
>> - value existence is known but actual value is unknown
>> - value does not exist
>> - value existence is not known 
>> So, your suggested split absent/unknown may not be the clearest.
>> 
>> I believe your Proposal 0 is implemented in the grammar.
>> 
>> I considered variants of Proposal 1 but ruled them out because the grammar was not ambiguous.
>> 
> 
> I would argue that the proliferation of different cases above is a strong motivation for cutting down on the number of cases.  Even if the grammar happens to be unambiguous (though I can't see how it can be), we are currently asking a lot of readers especially since the grammar is the last of the three documents they'll see.  
> 
> In an open world setting (I think!) we shouldn't distinguish between "value does not exist" and "value existence is not known".

+1


>  Combining provenance records could fill in unknown vlaues.  In any case, we currently have no way to express this distinction - and we don't say anywhere what should happen if we somehow learn the value of a "value that does not exist".
> 
> I also see no reason to distinguish between "value exists and is known but not expressed" and "value existence is known but actual value is unknown" - from the point of view of a consumer of provenance, what would I do differently?

+1

-Tim
Received on Thursday, 19 April 2012 12:26:03 GMT

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