IVOA Provenance DM -RFC- answers to comments

[Ole Streicher]

Hi all,

On 26.11.18 14:14, Ole Streicher wrote:
> On 22.11.18 14:59, Markus Demleitner wrote:
>> On Wed, Nov 21, 2018 at 05:45:56PM +0100, Mathieu Servillat wrote:
>> If we have that and find wasDerivedFrom is still worth it, I'm fine
>> with keeping it in.
> 
> In many astronomical uses, there is an indicator that the inputs of an
> activity are not equal: the "DATE-OBS" field (and similar others) in the
> FITS header. Obviously, for many activities there is one input where the
> DATE-OBS field is preserved in the output, while for the others, it is
> removed. I could guess that this one (or few) inputs is what people
> usually refer as the "main progenitor".
> 
> However, IMO this is a specific attribute of the "usage" for that input
> and not a special relation. When we can agree on putting this as a usage
> category (no idea for a good name, however), then we could solve the use
> case "I want to trace back my exposure to its raw input".
> 
> Independent of this, both wasDerivedFrom and wasInformedBy have some
> uses: One standard use is f.e. when the activity is a "Selector".
> Imagine an Activity selects (based f.e. on time) the right calibration
> data set, and you want to document that in prov: Then the selected
> Entity "was derived from" one of its input entities. You can't put that
> into a role; it is additional information.

On our telecon yesterday we had a short discussion about this, and Mark
convinced me that these use cases are rather theoretical for the moment.

It may be better to simplify our model in the first standards version by
removing wasDerivedFrom and wasInformedBy, and to use the following
solutions:

* use the "category" attribute of usedDescription to mark the "main
progenitor(s)". The definition and name of this category (as part of the
"category" vocabulary) could be left to the local implementation in the
first version.

* Always put an Activity between two Entities where one was derived from
the other, and use "used" and "wasGeneratedBy": f.e.
 - a "manual edit" Activity when one wants to mark the relation between
two consecutive versions of a config file
 - an "update" Activity for the relation between two ActivityDescriptions

* Always put an Entity between two Activities to carry the information
between them, f.e. a trigger. This will however require that we define
an Entity type for which we doesn't have neither value nor location.

* "Shortcuts" cannot be resolved this way, so it remains open how one
can provide several levels of detail of the same provenance.

Best

Ole