Schema instance documents

[Matthew Graham]

Hi,

The advantage of the schema at the moment is that it prevents people from
sending valid documents with empty fields, such as:

<resource created='' status=''>
  <vr:type/>

and thus ending up with empty entries for important metadata in the
registries. Allowing nillability would lose us this but make life easier
for some tools (although Ray is correct is saying that attributes cannot
be nillable (this might appear in XSD 1.1)). 

If we agree that nillability is not desired then can we come up with some
rules on dummy values to be in its stead, e.g. dates: 1970-01-01-00:00:00,
floats: -99999999. This way tools that need to produce valid empty content
instance documents have a way to do so and ingestors of the documents can
translate these dummy values to 'NOT PROVIDED' or however else they would
handle empty fields.

	Cheers,

	Matthew