(r7) DataLink11RFC < IVOA

IVOA Web>IvoaTCG>DataLink11RFC (revision 7)~~EditAttach~~

DataLink 1.1 Proposed Recommendation: Request for Comments

Introduction

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
Service descriptors can include exampleURL and contentType param(s), as well as DESCRIPTION, name, etc...
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
Added content_qualifier FIELD to inform on the nature of the link target
Added local_semantics to identify similar links in the same DataLink service for different IDs
Mechanisms to recognize {links} endpoints outside ObsCore

Latest version of DataLink can be found at:

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

The GitHub repository for issues and source can be found at:

https://github.com/ivoa-std/DataLink

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)

IRIS image: https://ws.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/caom2ops/datalink?ID=ivo://cadc.nrc.ca/IRIS?f212h000/IRAS-25um shows link_auth=optional and link_authorized=true because one can authenticate but the data is public.

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 v4.8-8 and later 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 Activation Actions suggested by topcat for the links not only depend on content_type but also content_qualifier, and local_semantics is used to guess which link a user is interested in based on previous selections.

AladinDesktop is going to adapt to those new features too. (see prototype screenshot)

The CADC DownloadManager (https://github.com/opencadc/apps.git) includes a simple DataLink client class so it can resolve publisherID values into 1..* URLs for download; this code hasn't changed as a result of DataLink -1.1. The CADC AdvancedSearch web portal makes calls to the above caom2ops/datalink service to find previews and download info for each row (publisherID): it makes use of link_authorized to decide to display the download options (or not), which prevents users from selecting downloads/links when they are not authorized and the request will be rejected later.

Implementations Validators

The following validators are available for DataLink

datalinklint which is part of STILTS. From STILTS v3.4-8 there is a version parameter that can be set to 1.0 or 1.1 (effectively defaults to v1.1)
Show my DataLink which is part of DaCHS

Comments from the IVOA Community during RFC/TCG review period: 2023-04-21 - 2023-05-18

The comments from the TCG members during the RFC/TCG review should be included in the next section.

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Comments from TCG member during the RFC/TCG Review Period: 2023-04-21 - 2023-05-18

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TCG Vote : 2023-05-19 - 2023-06-01

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