Datalink feedback II: RESOURCE type

[Markus Demleitner]

Dear DAL group, Dear Apps group

I crosspost this as this is largely a VOTable issue.  Also, this is a
welcome opportunity to point people not on the DAL list to 
http://www.ivoa.net/pipermail/dal/2014-March/006734.html -- I
consider the question of fixing suboptimal VO practices in service
parameter form *really* important and highly relevant to Apps, too,
so let me cordially invite you to comment there, too.

The issue at hand: The current Datalink WD says services are to be
described in elements like

<RESOURCE type="servce">...</RESOURCE>

It turns out RESOURCE type="service" may not be VOTable-legal.

Actually, it's a bit tricky.  In VOTable, the schema is not
normative, the spec text is.  Here is what it has to say about type:

  [A RESOURCE] may also be qualified by type="meta", meaning that the
  resource is descriptive only, i.e. does not contain any actual data: no
  DATA element should exist in any of its sub-elements. A RESOURCE without
  this attribute may however have no DATA sub-element.

The text does not mention type="results" at all as far as I can tell.

On the other hand, the schema says type defaults to results, which means
that technically, the type="results" thing we have in our DAL responses
wouldn't be necessary at all *if* we took the standard seriously.

My take: The situation is confused enough to say the restriction on
type should be lifted in the schema with the next VOTable release,
presumably together with the default specification that nobody should
have relied upon in the first place.  Meanwhile, the normative text
doesn't keep us from using type="service", so I'd say we're fine.

An obvious alternative might be to use utypes (and then
type="metadata"), but I'd much prefer if we could keep improvised
utypes out of datalink until there's clearly no choice.

Cheers,

          Markus