WasDerivedFrom vs. WasGeneratedBy

[Kristin Riebe]

Hi Markus, DM,

> But isn't the provenance structure in this case something like (notation
> contrived, roles suppressed in this graph -- imagine labels on the
> vertices if you will)
> 
> rawim2001 -- Photoproc ----- im2001 -,
>                /                       \
>    Flatfield and such                   \
>                \                         \
> rawim2002 -- Photoproc ----- im2002 ---- Coaddition --- coadd10001
>                                          /
> im1   --,                              /
> ...   ----- Calibration -- wcs -------/
> im1000--/     /
>          sectractor conf
> 

I would have expected that the wcs is applied to im2001 and im2002 
before the coaddition, but that's just a side remark. It seems by not 
using wasDerivedFrom we could force people to record the provenance of 
what they are doing more clearly, which would be a benefit.

> So, if you just look at the immediate operation of the co-addition,
> you'll succintly see that there were two reduced images and a WCS
> calibration coming in.  Only when you're interested in where that
> calibration comes from you see the 1000 images, at it should be, and
> just as you don't see the raw images as sources in the coaddition if
> the stacking was performed on flatfielded and darkframed images.
> 
> Similarly, in Ole's example:
> [...]

> I argue it's more straightforward to inspect the photo processing
> activity and figure out what the input with the role "raw image" was.
> After all, you might just as well suspect that the flat for this day
> was flawed and you'd just like to drop in yesterday's flat, or that
> any other gear in the provenance chain is at fault, and you might
> just as well want to replace that.
> 
> Sure, you'll have to define roles in this world for all inputs to all
> activities, but I'm sure you want that anyway.

Okay, you may get away with just defining roles well enough. In that 
sense wasDerivedFrom could be considered as just being an "optimization".
If we expect that users always want to have the big provenance chain of 
activities and entities that lead from a raw image to the final product, 
and not just the raw image, then indeed no short-cuts with 
wasDerivedFrom are needed.

Cheers,
Kristin

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Dr. Kristin Riebe
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