Datalink feedback II: RESOURCE type

[Patrick Dowler]

Hi Markus,

I was quite surprised when I ran into this in trying to create and 
consume DataLink tables and found that type could only take values of 
results or meta. (Checking... Ah. I even added a comment in Section 4.1 
of the last DataLink WD about this, repeated here:

--
Below we describe resources that describe services by setting the type 
attribute to the value “service”. However, the VOTable schema only 
allows “results” and “meta” as values for type. Do we ask for a new 
value to be added to the enumeration? Do we just use “meta”? If so, do 
we add something else to the RESOURCE so clients can tell it is a 
service description?
--


Right now we will have to use RESOURCE type="meta" to make things work 
in prototypes.


Pat


On 21/03/14 02:28 AM, Markus Demleitner wrote:
> 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
>

-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
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Victoria, BC V9E 2E7

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