DataLink issues

[François Bonnarel]

Dear all,
        Last interop confirmed there was interest in the DataLink 
concept , defined as a "way to find related resources to datasets via a 
web service"
       This is needed either as a complement to Data services (ObsTap, 
Tap, S*A service) or to SimDal...
A general agreement was made on input/output (PublisherDID/ VOtable with 
links) and on a general concept for the structure of the links "records"

There are  still a couple of issues, however:

          -- Is "DataLink" a real full DAL service with recording in the 
IVOA registries ? Or is just a web service refered in the main services 
query responses ?
The  first case requires  dataset ID to be a real PublisherDID. For the 
latter case an internal  DatasetID could be sufficient....

         -- One of our use cases is "related access to another DAL 
service". Another one  "Internal access  to complex datasets (archives, 
MEFS ....)....
The first use case can be some "AccessData" method of the DAL service 
performing some dynamic transformation on the dataset. The actual 
transformation is
  driven by the parameters values of the method. Probably "AccessData" 
URL of the service, without any parameter, could answer with a VOTABLE 
describing available parameters for the dataset...
             For the internal access to complex datasets, the May 2012 
DataLink draft proposed a little model for internal structure "mappable" 
on response VOTABLE FIELDs
This has been criticized as an "ad hoc" solution for our MEF or tar 
archives examples...
             Another solution could be "extended URI" (Norman Gray 
proposal). But the rightmost part of the URI is not interpretable anyway...
             A new proposal (Laurent Michel) could be that the link to 
the complex dataset  provides a list of parameters allowing to extract 
the various subparts of the dataset.
Something rather similar to the "AccessData" link behavior, eventually


Your comments are welcomed. We have to modify the May draft to go 
forward at netx interop

Best regards
François