Cube model - Dataset IDs

[CresitelloDittmar, Mark]

All,

I'm working to get an update to the cube docs out and have a question based
on Marcus' inputs to the Spectral doc.

Dataset Metadata has 3 dataset IDs defined, which originate from the
ObsCore and Spectrum docs.
  1) Curation.publisherDID
       obscore: IVOA ID assigned by publisher
       spectrum: string locating dataset within publisher holdings
       ssa: IVOA ID assigned by publisher, with no meaning outside that
namespace.

  2) DataID.datasetID
      obscore: <not in obscore>
      spectrum: IVOA ID assigned by publisher
      ssa: IVOA ID assigned by publisher (or maybe someone else?)

  3) DataID.creatorDID
      all: IVOA ID assigned by creator

The question is in the distinction between 1 & 2.
The best I can gather is in persistence.  The Curation.publisherDID can
change over time, while
the DataID.datasetID is supposed to be persistent.  If the publisher
re-locates the dataset, or changes the interface, this could effect the
publisherDID, but shouldn't effect the datasetID.  The datasetID folds in
the possibility of being an journal based ID (e.g. from ADS) to provide a
static ID.  (Note: Obscore does state that the publisherDID should remain
static through time.)

I'm not sure what to do with these.. are they both still necessary? or have
the usages crystalized enough to consolidate them?  It looks like TAP
services must rely on Curation.publisherDID, with the expectation that it
is static.  The SSA/SIA services have, I think, both, and appear to rely on
publisherDID more.

I'm leaning heavily toward Markus' suggestion to consolidate them.. drop
DataID.datasetID.
Describe Curation.publisherDID as an IVOA ID (therefore globally unique
since the publisher has a unique authority id), which identifies the
dataset within the publisher's holdings.  The ID should be persistent and
may be a journal-based ID (eg. from ADS).  The same dataset published at
multiple locations would have different publisherDID, but the same
creatorDID.

Thoughts?
Mark
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