SCS2: Text error messages; New: VERB

[Gregory Mantelet]

Le 08/07/2026 à 14:37, Mark Taylor via dal a écrit :
> On Tue, 30 Jun 2026, Markus Demleitner via dal wrote:
>
>> hope for Pat's DALI-text spec and move on to the next item in
>> Stelios' list:
>>
>>> 4. VERB semantics
>>>
>>> The spec says VERB must be "supported" but then says: "It is legal
>>> to always return the same set of columns independent of the value
>>> of VERB." which seems to undermine the parameter's usefulness.
>>>
>>> If implementations can treat VERB=1 and VERB=3 identically, clients
>>> cannot rely on VERB to reduce response size.
>>>
>>> How about specifying the minimum column requirements per VERB level
>>> (e.g., VERB=1 MUST include at least the three core columns, VERB=3
>>> MUST return all columns the service holds) and specifying that the
>>> default when VERB is absent is equivalent to VERB=2?
>>>
>>> Either that or why don't we just deprecate VERB entirely?
>> Well, I would have liked to drop VERB, as I don't think there have
>> been many conscious uses of it.
>>
>> On the other hand, I found the objection at the Interop convincing
>> that modern large-scale catalogues tend to have hundreds of columns
>> and having a way to control the chattyness *for them* would really be
>> useful.
>>
>> I buy that (although I can only encourage everyone to adopt arrays,
>> which often help keep metadata schema sizes sane).
>>
>> So, turning this around: Is it bad if clients "cannot rely on VERB to
>> reduce response size"?  What could they do if the could?  If you are
>> retrieving a catalogue that only has 10 columns, would you care?
>>
>> If you'd like to make this a bit more formal, one could formulate a
>> monotonicity condition: "Services must return all columns present in
>> VERB-1 at VERB (and may add more)" or something like this.  But even
>> there I'm couldn't give a strong reason to require this
>> (cf. <http://blog.g-vo.org/requirements-and-validators.html>).
>>
>> So... perhaps we can leave VERB as it is?
> +1 on leaving it as it is.  Yes VERB is ignored by some services,
> but nothing breaks in that case.  It's useful as a non-binding hint.
> I don't think anything would be gained (except keeping the validator
> authors in work :-]) by imposing hard requirements on how services
> have to interpret it.

+1 on keeping VERB. Sorry to answer so late.
I agree on two things based on my experience with Simbad, a bit of 
VizieR and Gaia:
1/ as user, being able to control the "chattyness of large-scale tables" 
becomes more and more important ; so, according to me, we definitely 
want to keep this feature,
2/ as a service developer, I agree that supporting 3 levels of verbosity 
is a supplementary burden, but it also helps to preserve the health of 
our database by limiting by default (VERB=2) the number of returned 
columns ; so, it worth it.

Grégory M.