Params cannot carry descriptions in VOEvent 1.1

[Rob Seaman]

> OK, this defines exactly what constitutes a Param (from the XML  
> Schema POV). It says that an element of type Param (<Param>) only  
> has four attributes: name, ucd, value and unit; and can contain  
> nothing else. No Description. No Reference.
>
> So:
>
> <Param name="Sun_Distance" value="132.21" unit="deg"  
> ucd="pos.angDistance">
> 	<Description>Angular distance from the sun to the event position</ 
> Description>
> </Param>
>
> is currently illegal (like dying in the Houses of Parliament).

This was intentional.  The specification is normative:

"Usage of <Param> and <Group> is similar to the VOTable specification,  
see §4.1 of [22]; however, a <Param> must be expressed as an empty  
element and only the following attributes are supported for<Param>  
under VOEvent: [name, value, unit, ucd]"

> Oh, and I've just noted that the schema also currently says that  
> elements can be called "Reference" but have no type associated with  
> them. This needs to be corrected as well.

The default interpretation for a missing type is url:

"3.9.2 type — The type of the document. Allowed values are "voevent",  
to reference a previously issued VOEvent packet (in whole or in part);  
"url", for a MIME-typed URL; "rtml", to refer to an RTML [15] document  
(typically the one used to drive the telescope that made the  
observation(s) resulting in the event), or — "ivorn", to refer to IVO  
resources. The default value is "url"."

The group needs to discuss what the behavior should be (and issues  
like the requirements for backwards compatibility).  Then the wording  
of a draft v2.0 specification needs to be vetted to match.  Then a  
draft v2.0 schema needs to be crafted to suit, and etc.

Some questions:

1) Is it the sense of the WG that Param elements should be permitted  
to have values?

2) If yes, are those values to be restricted to nested <Description>  
and <Reference>?

3) One of each or more than one of each?

4) What are the use cases driving more complex Params?  One might have  
thought that one point of SimpleTimeSeries and the proposed  
SimpleTables was to avoid making grouped params more complex than they  
already are.

5) Roy and Matthew have suggested that open-ended typing be permitted  
for references.  If so, does it make sense to require that a type must  
be provided?

6) Should a reference retain a default interpretation as a url?

Rob

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