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Re: prov-wg: Telecon Agenda March 8, 2012

From: Luc Moreau <L.Moreau@ecs.soton.ac.uk>
Date: Thu, 08 Mar 2012 15:44:47 +0000
Message-ID: <EMEW3|9eade25bc2d6e6be65dfe25df1b1d8f0o27Fip08L.Moreau|ecs.soton.ac.uk|4F58D3EF.60000@ecs.soton.ac.uk>
To: public-prov-wg@w3.org
Hi Curt,

Responses below,

On 03/08/2012 02:35 PM, Curt Tilmes wrote:
> On 03/08/2012 06:26 AM, Graham Klyne wrote:
>> Luc, thanks ... comments below:
>>
>> Re:
>> http://dvcs.w3.org/hg/prov/raw-file/default/model/working-copy/wd5-prov-dm-derivation.html 
>>
>
> [...]
>
>> In section 1, I'm still seeing a description that doesn't match the
>> sample ASN (e.g. which of the listed values does "e2" correspond to,
>> etc.)
>
> Yes especially when the description in the examples is simply:
>
>   "The first and second lines are about derivations between e2 and
>   e1."
>
> We need to make it very clear which is the "generatedEntity" and which
> is the "usedEntity".  Using those terms instead of simply e1,e2 make
> that more clear, or use a description for the example worded more like
> the third "using the entity e1 ... derived the entity e2" to make the
> direction of the derivation explicit.

Good point. I have updated the text in the example accordingly.

>
> I think Graham is suggesting that the terms in the ASN template match
> the terms in the term description list.  It currently requires the
> reader to match up "e2" with "generatedEntity" and "e1" with
> "usedEntity" by their order in the list.  It also seems awkward to use
> the '2' in 'g2' and 1 in 'u1' to associate the usage with e1 and the
> generation with e2.  Using common terms rather than relying matching
> order might make it easier (i.e. more clear) on the user.
>
>

I have now made it clear which parameter is which in the definition.

>> The first two look reasonable to me, but I still don't see why
>> wasDerivedFrom(e2,e1,a,g2,u1) is needed.  Once we have expressions
>> that explicitly name activities, how much real value is there in
>> having the "short cut" form?  Can't this be expressed by having an
>> explicit activity record, etc.?
>>
>> (I'm not suggesting the model should not be capable of expressing
>> this information, just arguing against this overloading of the
>> wasDerivedFrom record which AIUI is primarily an entity-entity
>> relation.)
>
> It does seem like bundling everything into one
> wasDerivedFrom(ie,e2,e1,a,g2,u1,attrs) is more complicated than simply
> requiring three distinct statements
>
>  wasDerivedFrom(id1,e2,e1,dattrs)
>  wasGeneratedBy(id2,e2,a,t2,gattrs)
>  used(id3,a,e1,t1,uattrs)

The problem is that you could have another usage

used(id4,a,e1,t1',u4attrs)

at a different time t1' not causing the derivation.

Also, a2 could also use e2 and generate e1 at the same time as a.

wasGeneratedBy(id2,e2,a2,t2,gattrs)
  used(id3,a2,e1,t1,uattrs)

So, it's essential to list the activity/usage/generation *in* the 
derivation expression.
>
> You state "The reason for optional information such as activity,
> generation, and usage to be linked to derivations is to aid analysis
> of provenance and to facilitate provenance-based reproducibility."
>
> Is that linking really required?  Within a single account couldn't you
> always infer that association?  I understand that different accounts
> might describe the activities at a different level of granularity and
> indicate, for example, that a single entity was generated by two
> different activities, but within a single account shouldn't it always
> be clear?  Even if it is possible for a DM user to express it
> unclearly, couldn't we just ask them not to with an explanatory
> section rather than simply giving them more rope?

I don't think we can infer this, even within an account. Multiple usages 
can be involved.
>
> Especially in the name of simplification, I wouldn't introduce this
> added complexity unless we can describe a clear case where it is
> needed.

Reproducibility of results is the key driver.  If we can't identify 
which activity, which usage, and which generation underpin a
derivation, we can't reproduce results.

Luc
>
> Curt
>

-- 
Professor Luc Moreau
Electronics and Computer Science   tel:   +44 23 8059 4487
University of Southampton          fax:   +44 23 8059 2865
Southampton SO17 1BJ               email: l.moreau@ecs.soton.ac.uk
United Kingdom                     http://www.ecs.soton.ac.uk/~lavm
Received on Thursday, 8 March 2012 15:45:25 GMT

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