VOEvent 2 TABLE mechanism

[Roy Williams]

Doug
Thanks for this. Perhaps I can just answer one point:

> A voevent table element can contain both PARAM and FIELD and these have
> a uniform set of metadata elements as in votable (name, datatype, unit,
> ucd, utype). This is all that is really needed in most cases. The main
> thing missing is GROUP.

Rob and I wondered about introducing this generality. As you say, it is 
an appealing idea. But I recall in the VOTable design how easy and 
satisfying it was to write that the RESOURCE could contain RESOURCE, ad 
infinitum, and how that recursion has burned us over the years (i.e. 
some code-binding fails).

However, as you say, it is a rare circumstance, and the customer can 
always create a Reference to some distant data object. So it was the 
usual strategy: lets keep it simple and see if anyone complains.

To summarize: the What section has two grouping constructs: Group and 
Table; and two data containers: Param and Field. A Field is like a Param 
but vector-valued, and all Fields in a Table have the same vector length.

Roy