#13 denoting unsupported values in results

[P.J. Schwartz]

We need to decide how to denote a column as
unsupported in results, versus having a null or empty
string value.

a null would look like:
<darwin:Collector xsi:nil="true"/>

an empty string would look like:
<darwin:Collector></darwin:Collector>

but how do we denote that a column was unsupported?
The desire would be to have:

<darwin:Collector supported="false"/>

but this has implications on the schema(s) that may be
undersirable. It would require for each element within
the federation schema the attribute be defined. May not
be pretty.

Other alternative might be to have a sentinal value that
meant unsupported, as in:

<darwin:Collector>UNSUPPORTED</darwin:Collector>

but this implies that for EACH datatype a sentinal value
would need to be defined. Its also bad because some
fields have range constraints and then it becomes really
difficult, especially for numerics.