ADQL - Careful what you wish for

[Jim Gray]

sage advice: 
 As one who has watched language designers struggle for many years with
languages like Fortran, VisiCalc, SQL, and HTML, I have learned that it
is not an occupation for dilettantes like us. 
So, to the extent that you can hijack an existing language like SQL, do
it. 
There are no "minor" changes to these languages; they all have any tight
interconnections. 
Adding XML data in the middle of some language is non trivial. 
If you really love XML, you might look at xQuery, but it has rather poor
implementations so far, and it lacks update/inset/delete; and some
describe the language as "ugly" . 
The Sky Query folks extended the table names with an extra level of
qualification and added a function (cross match).
That was safe and easy. 
I recommend you try to  use SQL's built in extension mechanisms.
It you really! want to do language design, do not couple that research
with the main path of the VO effort. 
It would make a fine side-project for the computer science guys -but it
should not be on the critical path for the VO 

Jim Gray
Microsoft Research,  Suite 1690, 455 Market, SF CA 94105,
tel: 415 778 8222 fax: 425 706 7329
Gray at Microsoft.com   http://research.Microsoft.com/~gray

-----Original Message-----
From: owner-voql at eso.org [mailto:owner-voql at eso.org] On Behalf Of Tony
Linde
Sent: Sunday, February 01, 2004 2:28 AM
To: 'Wil O'Mullane'
Cc: voql at ivoa.net
Subject: RE: ADQL - it aint so great

> Personally I also do not feel we need an XML form of ADQL. 
> But at IVOA meetings there was a general request to have ADQL in XML 
> format. I made a stab at and XML format. Modified it

I still think we need the xml version. Astronomy includes values which
are not simple scalars; representing structures even as simple as a
polar coordinate is messy in a textual language. As we add more complex
features/funcitons to ADQL we don't want to have to invent text
equivalents of vectors, arrays and more complex structured values.

An xml document is also easier to construct from user selections in a
query screen and much easier to translate into the many variants of SQL
(and OQL and ...) that are used in astronomical repositories since you
don't have to deconstruct the textual version first.

Personally I'd drop the textual version of ADQL - if anyone wants to
type the query in textual form, provide a pass-through option so they
can type the end repository's SQL query (or whatever language it
requires). (If they want the same query to go to multiple databases then
they either construct ADQL using whatever portal front end they prefer
or they type all the queries in manually.)

Cheers,
Tony. 

> -----Original Message-----
> From: owner-voql at eso.org [mailto:owner-voql at eso.org] On Behalf Of Wil 
> O'Mullane
> Sent: 31 January 2004 19:27
> Cc: voql at ivoa.net
> Subject: Re: ADQL - it aint so great
> 
> 
> Personally I also do not feel we need an XML form of ADQL. 
> But at IVOA meetings there was a general request to have ADQL in XML 
> format. I made a stab at and XML format. Modified it etc ... This of 
> course may be discussed again at the meeting.
> Even internal to SkyServer there is some parsing going on as Clive 
> suggests. People generally felt having a parsed version would help in 
> this area.
> 
> 
> We are aware of some of the problems mentioned especially with 
> java. Vivek is currently working on this and I believe will 
> post some new tutorials etc in the coming days.
> 
> 
> wil
> 
> 
> On Sat, Jan 31, 2004 at 04:40:11PM +0000, Clive Page wrote:
> > On Fri, 30 Jan 2004, Noel Winstanley wrote:
> > 
> > >   I tried and I failed.
> > >
> > > I can;t get any joy with the latest version of ADQL.
> > 
> > > I'm really beginning to wonder whether ADQL is the most suitable 
> > > query language for astrogrid datacenters. What are its benefits?
> > 
> > I agree with your comments, Noel, and I've been asking for 
> some time 
> > why we need ADQL.  The only answer I was able to get was 
> that it made 
> > the checking of the query simpler and improves security.  I am not 
> > convinced that we need to be all that fussy in checing 
> syntax: if the 
> > user generates the query from our menu-style registry-driven portal 
> > then it will be hard to make a syntax mistake; power users who 
> > generate their own SQL by typing it into a text box will 
> find out soon 
> > enough if they make a mistake: any DBMS parses the query 
> and returns 
> > an error message instantly.  The experience of JHU with their 
> > skyserver was given at the last ADASS meeting by Wil 
> O'Mullane: indeed 
> > he made a mistake in his live demo and got a message back, allowing 
> > him to correct it.  This isn't a perfectly user-friendly 
> system, but 
> > it seems adequate to me.  As far as security goes, a simple 
> solution 
> > initially is to restrict the first keyword of any query to 
> be SELECT, 
> > and in particular prevent non-authenticated users from 
> issuing DROP or 
> > DELETE statements.  Later, maybe, we can allow things like CREATE 
> > TABLE, INSERT, UPDATE, and so on.  That shouldn't be all that hard 
> > even without ADQL.
> > 
> > 
> > --
> > Clive Page
> > Dept of Physics & Astronomy,
> > University of Leicester,    Tel +44 116 252 3551
> > Leicester, LE1 7RH,  U.K.   Fax +44 116 252 3311
>