Subject: Re: More Stateless Catalog use cases
Resent-Date: Thu, 31 May 2001 10:54:54 -0500 (EST)
Resent-From: servicemodel@opengis.org
Date: Thu, 31 May 2001 12:04:22 -0400 (EDT)
From: Jeff de La Beaujardiere <delabeau@iniki.gsfc.nasa.gov>
To: Doug Nebert <ddnebert@fgdc.gov>
CC: Service Model <servicemodel@opengis.org>, catalog.wg@opengis.org

Doug Nebert writes:
> Two Stateless or Stateful Catalog Use Cases: Search for
> Map Invocation

> Option 1:
> [...]
> o The handle is used to fetch the valid parameters for the
> invocation of the map service instance, coupled with the
> layer name stored in the data metadata as a qualifier.

I believe this almost works as long as what you are fetching
are valid parameter *values*, not valid parameters and their
values, because applications will need to know the service
types and their parameters at software design time, not at
run time.

I say "almost works" because some things are not simply cast
as enumerations of valid parameter values (Bounding Box is
one example).  You need a good way to represent those
validity constraints.  I'm not sure we found the right way
to do it in the ISO 19119 discussion ("Operations" and
"Content" sections with Xpointers between them), and I'm
sure that you need the information at design time.

> Option 2:
> [...]
> o The capabilities are fetched directly from the map
> service provider

The problem here is that at least one WMS has a 1.3MB
Capabilities file containing over 1500 <Layer> elements.  We
need a way to get a single-object subset of that information
either from the Catalog or directly from the WMS.  For the
latter, something like
SERVICE=WMS&REQUEST=GetCapabilities&LAYER=layer or
SERVICE=WMS&REQUEST=GetCapabilities&FILTER=filter would be
useful.

Regards,
Jeff DLB