IVOA Simple Line Access Protocol v0.2

[Jesus J. Salgado]

Hi Doug,

Your approach looks good. Pedro and I were thinking in a similar
approach but using brackets and parenthesis to define domains (in the
same way that is done in standard calculus). For example, using a
notation close to yours:

param=[3:5)

(values in range from 3 to 5, including 3 but not including 5)

param=[3:5],[7:)

(values in range from 3 to 5 including both OR range from 7 to infinite
including 7)

As the "," means "OR" in the final SQL sentence, we have been thinking
if other logical operators are needed, but probably the current
definition is enough, as the "AND" is used more often for the
combination of queries for different parameters, e.g.

param1=[3:5],[7:)&param2=(1000,3000]

means:

(param1 values in range from 3 to 5 including both [OR] range from 7 to
infinite including 7) [AND] (param2 values in range from 1000 to 3000
including 3000)

Depending on the type of variable and the rounding error, the difference
between open and close ranges might be more or less relevant; so
probably, as your approach is easier to parse, we can adopt your
definition for the wavelength range in the SLAP. 

Best Regards,
Jesus


On Wed, 2006-02-08 at 17:48, Doug Tody wrote:
> 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
-- 
Jesus J. Salgado


ESAC Science Archive Team
e-mail: Jesus.Salgado at sciops.esa.int
Tel + 34 91 8131271

European Space Agency/European Space Astronomy Centre
VILLAFRANCA Satellites Tracking Station
P.O. Box 50727
E-28080 Villafranca del Castillo
MADRID - SPAIN