comments on ADQL draft
roy at cacr.caltech.edu
Tue May 6 06:56:17 PDT 2008
(1) The standard as given is very simple in terms of coordinate frames
etc -- assumes all handled elsewhere. What should a user do if they wish
to query a table that is in galactic coordinates or B1950.0? What if the
user wishes to write queries in other coordinate systems?
(2) The functions defined in the paper have poor extensibility because
of these fixed fortran-like arguments. Why not plan for the future
extension of the standard, and also make things more readable, with
something like this:
POINT(frame="ICRS" equinox="1950" position2d="270.0, 22.0")
(3) The given document is difficult to read with its single-minded focus
on bulding a BNF grammar. It needs examples to show the semantics and
semiotics of the BNF statements. Without examples it is difficult for me
to understand semantics: either how customers might respond, *or* how
difficult it is to implement. How, for example is the LONGITUDE(POINT)
-- Can I say this:
SELECT * from Table where LONGITUDE(POINT) between 270 and 285
If so, what kind of tables have POINT structures in them?
-- Can I say this to implement a SIAP?
SELECT * from ImageTable where INTERSECT(POLYGON, SDSS_DR6_FOOTPRINT)
-- Can I say
SELECT POLYGON from ImageTable
What kind of tables can be interpreted to have POLYGON attributes?
(4) What kind of table can I specify in the select clause? Can I use
VOSpace, like this:
SELECT * vos://nvo.caltech.edu/myTable.dat where INNER JOIN SDSS_DR6
I ask this, because the DAL group is assuming that everyone will have a
VOSpace that can provide temporary storage, and that crossmatches are
done through ADQL queries. An alternative is for VOQL services to allow
qualified users to upload tables, like CasJobs.
(5) There is already a specification of spatial regions (*) that is
semantically identical to the STC standard, which is and IVOA
But the definitions in the ADQL document use different words and
different meanings from this, (eg one says BOX and the other says
RECTANGLE). Have the ADQL authors read the existing IVOA standards? If
so, what has been inherited from the STC standard into the ADQL?
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