IVOA Simple Line Access Protocol v0.2

[Doug Tody]

A simple approach to range lists which requires only a slight departure
from what is currently done in SIA (POS) and proposed for SSA is to keep
"," as the list delimiter but switch to another metacharacter, ":" perhaps,
for ranges.  Then we have

     param = x				equality
     param = x:y				closed range
     param = x:				open range
     param = x,y				list
     param = x,a:b,y			range list
 	etc.

For example, for a list of wavelength ranges (one of our SIA cube access
use cases) we would have

     wavelength=w1a:w1b,w2a:w2b,w3a:w3b,...

This approach can also be used for simple abstract datatypes, e.g.,

     wavelength=w1:w2,source

could specify wavelength in vacuum in the rest frame of the source.

The semantics would be defined on a per-parameter basis.  One advantage of
this approach is that the semantics are defined by the parameter and hence
are protocol independent; the same string can be passed through from the
client to the server regardless of the protocol used (URL, WSDL, parameter
file, Java RMI, XML RPC, etc.).  The atomic nature of encoded parameter
values helps here.  Once again, for a fully general approach we can use
a language approach instead (ADQL) so we want to keep this fairly simple.
Quite a lot can be done with a simple parameter-based interface however.

 	- Doug