Rethink the Constraint-based search Query from Registry interface

[Paul Harrison]

Ray Plante wrote:

> Okay, you're a brave soul.  
> 
> Before we get too deep into what's wrong with ADQL and XPath, let's step 
> back and look at requirements and constraints which presumably led to this 
> choice.  

It was not intended to be an argument about what is wrong with ADQL and 
XPATH - As my opening statement makes clear I was one of the "XML 
purists" that felt the registry would be a more powerful and flexible 
tool if it were pure XML and used XQuery as the query language, but I 
accept that argument is lost.

I was really arguing for I guess, although I did not say it explicitly, 
was that we have a separately defined registry query language, and a 
simple one at that without all the XML syntax. But, given that it is 
late in the day for major reworking, we base it on what we have. 
However,  instead of the standard making reference to ADQL and XPath, 
with restrictions, we should branch the bits of ADQL that the query 
actually uses, make the necessary technical changes to the schema in 
order to remove the need for the restrictions mentioned in the standard, 
and call it RQL - we can then even encode the format of the restricted 
XPath-like "column names" in the schema. Separating the evolutionary 
paths for the query languages at this point will allow a registry query 
language to add specializations particular to the registry without being 
burdened by  having constantly to squeeze into the rdb model that ADQL 
supports.


Paul.


-- 
Paul Harrison
ESO Garching
www.eso.org