DataLink RFC period annoucment

[Pierre Fernique]

Dear DAL members,
Concerning the Datalink RFC, I have one general comment, a few technical 
questions, and a wish.

*1) General comment:*
Despite the introduction,  the difference between the two datalink 
methods has not be clear for me. Both are called "datalink" and it is 
difficult to understand the difference between the two methods with the 
same name.  I suspect that there were various author point of views and 
no definitive choice. Why and when we have to use one method or the 
other one would be helpful for future implementors.

*2) Technical questions:* Concerning the second method (with the  PARAM 
definitions by GROUP):
The possibilities opened by this method is very promising. At the first 
view, it seems simple and flexible, and very useful to build on the fly 
associated user forms.

a) However, I do not see how to describe REST links, or any URL for 
which the prefix depends of the parameter values. May be I'm wrong, but 
it seems that this method can only build URL on this template : 
http://static_url_prefix?param1=val1&param2=val2...
However, it is quite common that some servers provide their collections 
on this basis URL template :
http://host/variable_path/datasetID (VOSpace links ?). It would be great 
if basis URLs could be also described by this datalink method.

b) Also, I did not find any thing concerning HTTP encoding requirements. 
May be a short paragraph could avoid some stupid future bugs (param=val 
must be correctly HTTP encoded..., the & character must be used as 
parameter separator)

c) One point concerning "blank or missing value". In my experience, 
some  servers have no ALL option for such or such parameter : just the 
lack of the HTTP "param=xxx" parameter meaning "ALL" for this 
constraint. Removing the "&param=" parameter of the URL in case of blank 
or missing value can be a solution for managing these cases.

*3) My wish. *
In IVOA we use frequently VOTable as a container (SIA, SSA, TAP, ObsTAP, 
and now Datalink), but without magic code or any signature to recognize 
that this VOTable is a Datalink result, or a TAP result or whatever. And 
concretely it is a nightmare for client which are supporting  
simultaneously several of these protocols. I recommend to introduce in 
our VOTable protocols (at least the new protocols) a signature which 
could be a simple INFO tag (ex: <INFO name="protocol" 
value="datalink1.0"/>).

Best regards
Pierre Fernique





Le 11/07/2014 18:58, François Bonnarel a écrit :
> Dear IVOA members and partcipants
>     I remind you that RFC period for DataLink started a week ago.
>     No comments have been produced so far
> Cheers
> François
> Le 04/07/2014 11:34, François Bonnarel a écrit :
>> Dear IVOA members and participants,
>>
>>         After several months of intensive discussion within the 
>> Working Group the DataLink Working draft has now reached the status 
>> of "proposed recommendation".
>>
>>         Thanks to Pat Dowler's editing work (taking into account the 
>> live ESAC spring interop discussions) and thanks to Sarah the new 
>> version of the specification document can be found here:
>>
>> http://www.ivoa.net/documents/DataLink/20140530/index.html
>>
>>         The "request for comments" period is starting today and will 
>> stop on Monday, September the 1st at midnight, immediatly followed by 
>> the 4 week TCG review period. If no serious issue is discovered 
>> during these two periods of comments and review, DataLink could 
>> become a recommendation at the fall interop time.
>>          You can find the RFC page there:
>>
>>          http://wiki.ivoa.net/twiki/bin/view/IVOA/Datalink1RFC
>>
>> Good comments work and best regards to everybody
>>
>> François Bonnarel
>> Marco Molinaro

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