resuming progress on TAP

[Keith Noddle]

> AdqlQuery (AQ) and ParamQuery (PQ) are *service operations*, not query
> languages, each of which accepts certain parameters and returns certain
> outputs, provides status returns in a certain way, etc.  Altogether
> this defines the service interface (an abstraction which is not at
> all specific to HTTP by the way, except for a mapping onto HTTP).
ADQL allows a user to define a query, I hope we are all agreed on that. 
We (DAL) are in the business of describing:

(1) A "Service", which is the *Application* the user wishes to use
(2) The "Service Interface", which describes *HOW* that application is 
invoked and used
(3) The "Payload", which defines *WHAT* we want the application to do.

Considering ADQL, this distinction is clear - it is the Payload. Doug 
was right to point out the LANG parameter because it provides the option 
for a TAP Service at some point in the future to support XQuery - 
another type of Payload that defines WHAT we want the service to do. Why 
then is a Parametrised Query any different? AQ, XQuery and PQ are 
queries; whether they are languages in the dictionary definition sense 
is irrelevant.

It is my contention that we confuse the PQ Service Interface with the PQ 
Payload because we tend to think in terms of HTTP calling. However, it 
would be equally valid for a Parametrised Query to be expressed as an 
ASCII file of Key-Value pairs for example. The Service Interface for 
this would define how the service accesses that file and thus consume 
its content. Keeping the HOW and the WHAT separate is the heart of Pat's 
proposal and Aurelien's posting.

Conflating the Service Interface with the Payload is the crux of the TAP 
issues, IMHO. Pat's proposal has neatly answered this conundrum - if we 
just take a moment to consider it in detail. We are agreed upon our end 
goals for TAP. The route we take to get there and the quality that 
results is ours to achieve.

-- 
Keith Noddle                    Phone:  +44 (0)116 223 1894
AstroGrid Project manager       Fax:    +44 (0)116 252 3311
Dept of Physics & Astronomy     Mobile: +44 (0)7721 926 461
University of Leicester         Skype:  keithnoddle
Leicester                       Email:  ktn at star.le.ac.uk
LE1 7RH, UK                     Web:    http://www.astrogrid.org