Approach to metadata for Spectral Data at the Planetary Data System (PDS)

[Markus Demleitner]

Hi Anne,

On Mon, Jun 14, 2021 at 10:44:49AM -0400, Anne Catherine Raugh wrote:
> The tags are documented as part of the PDS4 Information model. They are
> part of the information model label taxonomy in what we call the
> "Primary_Result_Summary" class. The formal definition from the Information
> Model (IM) is here:
> 
> https://pds.nasa.gov/datastandards/documents/dd/current/PDS4_PDS_DD_1G00.html#d5e15413

This points to a ToC entry for me, which then points to 
https://pds.nasa.gov/datastandards/documents/dd/current/PDS4_PDS_DD_1G00.html#d5e85

-- and that I find intriguing, because its terms seem to be much
closer to what for us is the relationship between a primary dataset
and component artefacts, which we keep in the datalink/core
vocabulary, http://www.ivoa.net/rdf/datalink/core.  I'm tempted to
try and match the two vocabularies to see what we might be missing.

Out of curiosity: Do you have statistics on how much the different
product types are being used, both in terms of depth ("how many are
there of each type?") and of breadth ("how many projects are offering
products of some type?")?

Oh, and: From "Class Hierarchy" it would see to me that your (in
effect) vocabulary is flat; for instance, I'd have expected to see
"Context" as somehow narrower than "Document".  Was it a conscious
design decision that it's not?

Closer to what we're trying in product-type is what I'm finding in
classes like "Array_2D_Spectrum", which also have a deep hierarchy
(cf.
https://pds.nasa.gov/datastandards/documents/dd/current/PDS4_PDS_DD_1G00.html#d5e3914
for an example).

What I couldn't quite work out there: Is there a way for a machine
(that, I think, would treat the class names as opaque) to work out
that Array_2D_Spectrum and Array_3D_Spectrum offer spectrally
resolved data?  And why is there no 1D spectrum?

I'm asking these questions because I'd *expect* (without actual
evidence) that "I need spectrally resolved information on X" is one
of the more common use cases in this field of data discovery, and
every time I think of it I reach a different opinion on whether it's
a good idea to serve users cubes when they were presumably expecting
to see plain ol' 1D spectra and their client programmes will just say
"Can't open your file".  Do you have any experience with user
expectations in one way or the other?


> It was a struggle to get metadata like this into the PDS4 Information
> Model, because historically PDS has only ever described its data in terms
> of its source (which instrument, which spacecraft, which mission) and its
> target (which planet, and even non-planet targets were problematic). So I
> view it as a start, but I hope we can do better for version 2.0.

Yeah -- good metadata is data altruism, as the data creators can do
without much of it during initial data exploitation.  So, I think
it's never an easy sell...

Thanks,

           Markus