ADQL v0.7.3

[Tony Linde]

We don't seem to be getting far on the ADQL v0.7.3 discussions. My main
concerns are about 'proving' the validity of the simplification and how we
manage ADQL in the future.

We need a clear statement of how the current v0.7.3 is generated (and also
how v0.7.1 aka 0.8 was generated). It seems that a SQL-92 BNF - SELECT only
- was put through some tool which created an xml schema version, BNF/x. This
was then modified to add cross match and region capability, giving ADQL/x.
This, effectively was the v0.7.1 version. This version was them 'simplified'
by losing some of the common structures (eg Search type) and coalescing
stacked elements into single ones; lets call this ADQL/sx.

Is this a correct summary?

If we're to standardise ADQL and we want the BNF to remain as the core, we
need to document and/or automate each of these transitions. All of the /x
--> /x transitions can be automated using XSLD, and the BNF --> BNF/x is
automated using the tool. 

Could Wil or Vivek please provide us with:
1. what is the exact BNF used and where was it sourced and how modified?
1. what is the name/location of the tool used to convert the BNF to BNF/x?
2. what modifications were made to convert BNF/x --> ADQL/x?
3. what modifications to ADQL/x were made to produce the simplified version,
ADQL/sx?

It doesn't make sense to me to introduce the extensive changes in the ADQL/x
--> ADQL/sx transition yet to say that changing the cardinality of
intersection & union searches from 2 to 2..* is invalid. 

Another question is how we manage the string version of ADQL, ADQL/s. It
should be a simple matter to convert a single instance of an ADQL/x query
(ADQ/x) into string form (ADQ/s) using XSL. But, if people want to allow
*direct entry* of the string version of ADQL and to parse ADQL/s then we
will need some way of generating a new BNF that corresponds to the modified
ADQL/x or ADQL/sx; this should be an automated method so that future
extensions can be incorporated easily.

Cheers,
Tony. 

__
Tony Linde                 
Phone:  +44 (0)116 223 1292    Mobile: +44 (0)7753 603356
Fax:    +44 (0)116 252 3311    Email:  ael at star.le.ac.uk
Post:   Department of Physics & Astronomy,
        University of Leicester
        Leicester, UK   LE1 7RH

Project Manager,            Director,
AstroGrid                   Leicester e-Science Centre
http://www.astrogrid.org    http://www.e-science.le.ac.uk/