[fitsbits] 'Dataset Identifications' postings (digest)

[Rob Seaman]

Interesting discussion.  It was not previously obvious how specific
a concept was being discussed.  Thanks to Arnold Rots for the details:

> The proposal is to introduce the DS_IDENT keyword as a convention for
> dataset identifiers and to define one particular set of values for
> this keyword - the ones under the autority of the ADS, i.e.,
> identifier values starting with "ADS/".  Anybody who wants to
> participate in the use of this convention is free to do so, but will
> have to comply with the the rules of that convention,

Wouldn't it make more sense to reserve a keyword called "ADSIDENT"?
That is the precise naming space that is being discussed.  If you stick
with DS_IDENT (or DS_IDn), you are implicitly assuming that a single
dataset (and the individual files that comprise that dataset) will
never benefit from being named by multiple certification entities
simultaneously.

> Of course, this begs two questions:

It begs more than two :-)

> - Can two files have the same DS_IDENT value?
> The answer should be yes, since a dataset may consist
> of more than one file.

The answer *must* be yes, because this possibility cannot be legislated
out of existence.

> - Can one file belong to more than one dataset?
> The answer is again yes.  This may mean that we should
> allow for DS_IDn keywords.

A file can belong to more than one ADS-style dataset.  A file can also
belong to more than one entirely distinct name space.

Suggestions:

1) Reserve ADSID and ADSIDn for the purposes of the proposal being
discussed.

2) Expect to reserve keywords of the form xxxIDn in the future for
similar purposes related to other certifying entities.

If the concept of ADS administered ID name spaces is of use to the
larger astronomical community, this will become obvious as other
data providers sign on to the ADS bandwagon.  Meanwhile, it may *also*
be useful for some data providers to form their own ID name spaces.

> (I said "files"; you may read "extensions", if you like)

Again - separate IDs *must* be supported for separate extensions.
How are you going to legislate against MEF files containing files (or
other data structures, such as tables) from more than one dataset?

> The question has come up in which headers the keyword should appear.
> I would recommend putting it in any and all headers where it is
> appropriate - primary and secondary.

Agreed!

> Hope this helps,

Yes, indeed.  Thank you, Arnold.

Rob Seaman
NOAO Science Data Systems