The scope of Tom's proposal is really quite limited:

He is announcing the establishment of a convention that employs
a keyword (DS_IDENT) or set of keywords (DS_IDiii).
The intent is that the value of that keyword contains a label or key
that will allow users to obtain a pointer to a particular volume in
astronomical data space. No less, but also no more.

Within the space of data identifier strings only the subspace of
strings starting with "ADS/" (case-insensitive!) is reserved.

That's really all; you can stop reading here. But if the subject
fascinates you, you may read on.

Anybody who wants to participate in that subspace needs to know a little
more (like the substring between the first '/' and the first '#' that
represents the facility from which the datasets originated, and the
fact that that facility is free in choosing its definition of what a
dataset is and the encoding of everything after the first '#'), but
that is not particularly relevant for this newsgroup.

"volume in data space" or "dataset" is left vague because it is up to
the issuing facility to decide what makes the most sense for its users
and purposes. For the Chandra Data Archive what you will get in
response to the key is a URL that will allow you to request a download
of data products associated with a particular observation - or maybe a
set of observations. If you try again next month, the files may be
different: we may have reprocessed or decided to add some products to
the package. For other archives it may be a specific file. For the
ADS itself, you may think of an OID as the label and a journal article
as the dataset.

There is no intent to prescribe the syntax or the semantics of the
identifiers. And there certainly is no intent to imply any kind of
inheritance or propagation of identifiers to the user level.

Again, think of the dataset identifier as a key that allows the user
to obtain a pointer to the dataset. There is no need to encode any
information in it - nor is that prohibited (the ADS could use bibcodes
as identifiers).

The list of informational metadata that Rob provided looks to me more
like metadata that ought to reside in a database. And if you wanted
to know what all the values are, you would take the NOAO dataset key
and query:

select * from RobsDatabase where DS_IDENT='NOAOidentifier';

where NOAOidentifier is something short and, possibly, random, rather
than trying to decode information from a string that stretches over
many header rows. Again in Chandra archive language, if you want to
browse that kind of information, you come to our web browser that will
query the database that contains the observation catalog; it will tell
you about objects, coordinates, times, observers, instruments,
proprietary times, public release dates, etc.

- Arnold

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Arnold H. Rots Chandra X-ray Science Center
Smithsonian Astrophysical Observatory tel: +1 617 496 7701
60 Garden Street, MS 67 fax: +1 617 495 7356
Cambridge, MA 02138
USA http://hea-www.harvard.edu/~arots/
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