Difference: DataLink11RFC (2 vs. 3)

DataLink 1.1 Proposed Recommendation: Request for Comments

DataLink describes the linking of data discovery metadata to access to the data itself, further detailed metadata, related resources, and to services that perform operations on the data.

The main changes in v1.1 are

• Generalize by adding use cases for links to content other than data files
• VOSI-availability and VOSI-capabilities endpoints are now optional

• Added optional link_auth and link_authorized to signal whether authentication is necessary to use the link
• INFO element with standardID mandatory in {links} response

• https://www.ivoa.net/documents/DataLink/20230413/index.html

Reference Interoperable Implementations

Server side

GAVO implemented the following changes = content_qualifier and local_semantics, service descriptor additional features such as DESCRIPTION? name, content_type, etc....

As a matter of example, a couple of links response for various obscore/sia/ssa tables in GAVO server

• rosat.images : http://dc.zah.uni-heidelberg.de/rosat/q/dl/dlmeta?ID=ivo%3a%2f%2forg.gavo.dc%2f~%3frosat%2fimage_data%2frda_4%2fwg400138p_n1_p1_r2_f2_p1%2frp400138n00_im3.fits.gz where some links have content_qualifier = #image, others have content_qualifier = #event or #timeseries
• lamost6.lrs : http://dc.zah.uni-heidelberg.de/lamost6/q/sdl_lrs/dlmeta?ID=ivo%3a%2f%2forg.gavo.dc%2f~%3flamost6%2flrs%2f373006237 where some links have content_qualifier = #spectrum
• califadr3.cubes : http://dc.zah.uni-heidelberg.de/califa/q3/dl/dlget?ID=ivo%3A//org.gavo.dc/~%3Fcalifa/datadr3/COMB/ARP220.COMB.rscube.fits where some links have content_qualifier = #cube
• ppakm31.maps : http://dc.zah.uni-heidelberg.de/ppakm31/q/cdl/dlmeta?ID=ivo%3a%2f%2forg.gavo.dc%2f~%3fppakm31%2fdata%2fPPAK_M31_F5_cube.fits wher some links have local_semantics filled up and content_qualifier equals #image or #cube

All these are combined with various semantics or content_type values

CADC has implemented the following in https://ws.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/caom2ops:

• INFO element with standardID in links response
• new optional fields in links response: local_semantics (no content yet but can be populated with default vocab in most cases), content_qualifier (no content, not likely to use), link_auth, link_authorized
• contentType param in service descriptors (where applicable)

new CFHT data: anonymous use of https://ws.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/caom2ops/datalink?ID=ivo://cadc.nrc.ca/CFHT?2773629/2773629o shows link_auth=optional and link_authorized=false because the data is still proprietary and the caller is anonymous; if an authorized user makes the call they will see authorized=true. It's hard to demonstrate that for a general audience.

The core CADC implementation is available as a library (cadc-datalink-server) in MavenCentral with source code at https://github.com/opencadc/dal.git; the caom2-specific logic is available in a library (caom2-datalink-server) with source at https://github.com/opencadc/caom2service.git -- the core lib is also used in ALMA DataLink service but may not yet be released with the latest features.

Client side

TopCAT prototype (http://andromeda.star.bristol.ac.uk/releases/topcat/pre/topcat-full_datalink11.jar) displays additional features in service descriptor and makes use of additional links table FIELD such as content_qualifier, authorization and local_semantics; The tool behavior is adapted to the content of these new FIELDS. For example Actions suggested by TopCat for the links not only depend on content_type but also from content_qualifier.

Implementations Validators

The following validators are available for DataLink

• DataLink Lint which is part of STILTS
• Show my DataLink which is part of DaCHS

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