[SIAv2] query params

[Patrick Dowler]

I completely agree with the following. If a spec supports 
custom/extension parameters that users are supposed to discover and make 
use of, we need a mechanism to describe these parameters.

It is true now that all DAL specs allow implementers to support 
extension parameters; people can build a compliant VO service and add a 
few extras to support their portal or UI without having to build two 
back-end services, so that it a big win.

Now: extension parameters need to be discovered and used by generic 
clients and arbitrary users. This is an open question and as far as I 
know not supported by the use cases. The use cases are all about what 
the client/user needs to be able to do and this concept of advertising 
what a service can do is more of a desire for service implementers to 
expose what they have rather than what the user community has asked for. 
I'm not saying it isn't valuable and I can certainly see that it would 
be nice to have.

* Questions *

1. Is there an established use case I am forgetting that says extension 
parameter support is essential for the initial SIAv2 query interface?

2. Do we *really* need this in 2.0? Can we wait for 2.x?
- it is true that if we adopt something like the proposed mechanisms for 
spatial/temporal/spectral query params that this impacts a param 
description to be developed later

Pat

PS -- I'll remind everyone that we have several working SIAv2 prototypes 
of the query interface and they are usable to do the queries in the use 
cases. That is what we are now standardising in 2.0 and we fully expect 
2.1 and 2.2 to follow after prototyping of new features.

On 12/02/2013 01:36 AM, Markus Demleitner wrote:
> Now, if we need some mechanism to describe extension parameters, I'd
> argue it should be good enough to be used for the standard
> parameters, too -- no special rules in the text, less language in the
> standard, less code in the implementation, profit all around.

-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9A 2L9

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