VOEvent - Param comment

[Ray Plante]

On Mon, 7 Aug 2006, Petr Kubanek wrote:
> You are making in my point-of-view classical XML-designers mistake. 

While your suggestion certainly has advantages, the best choice is not
obvious.

> <Param name="TRIGGER_NUM" value="114299" ucd="meta.id" />
> <Param name="RATE_SIGNIF" value="20.49"  ucd="stat.snr" />
> <Param name="GRB_INTEN  " value="73288"  ucd="phot.count" />
> 
> Let's have something like:
> 
> <GRB>
>   <trigger_num>114299</trigger_num>
>   <rate_signif>20.49</rate_signif>
>   <grb_inten>73288</grb_intent>
> </GRB>

The difference here is between what I call a generic container and a 
semantic container.  The latter is helpful when the scope of meaning is 
well contained.  As you allude, a generic container is necessary when you 
can't constrain the semantics at the time the schema is defined, perhaps 
because it may change either depending on the application or just over 
time.  In my experience, sometimes the advantage of Schema-based 
validation works against you in the face of this change.

If we are to have interoperable semantics that allow machines to interpret
these terms, then the terms must be well documented and
standardized--whether they are part of the XML Schema or not.  

(BTW, just to avoid confusion, UCD refers to the values of the ucd 
attribute.)

cheers,
Ray