*IVOA DAL WG Running Meeting
29 June 2020 - 20:00 UTC - vconf

Participants: (13) Marco Molinaro, James Dempsey, Jon Juaristi Campillo, François Bonnarel, Laurent Michel, Renaud Savalle, Mark Taylor, Serge Monkevitz, Pat Dowler, Brent Miszalski, Jesus Salgado, Gregory Dubois-Felsmann, Tom Donaldson

*Agenda:
	1. DALI-1.2 roadmap
	1. UDF Catalogue EN:
	1. DataLink templated endpoints
	1. Running Meetings brainstorming
    
*Notes
1 - DALI
3 issues after Groningen added to the GitHub repo
PR reflecting some new sessions.

MAXREC wrt DataLink issue.
Separate issue about overflow indicators in DALI.
Should be only clarification.

xtype(s) are what needed for ADQL.

multipolygon separator was undecided...requires prototyping to solve.
Pat can volunteer 1 prototype (server)

simplified version for shapes wrt STC-S
xtypes are not trying to point to STC-S directly.
If ADQL:REGION is used after DALI-1.2 that's still valid and coped with wrt TAP-1.0 definition.
MT: need a place in ADQL to specify this. Or maybe add a footnote to DALI-1.2 to specify/clarify this.

FB: ObsCore has text saying that s_region are ADQL:REGION -> might need an ObsCore revision
JD: This is in sections 4 and 4.12 of REC-ObsCore-v1.1
	* MT: but slightly subtle: ObsCore mandates it as ADQL:REGION always, but as STC-S only for TAP 1.0

2. UDF catalogue EN:
	* Current document: http://ivoa.net/documents/udf-catalogue/20190925/PEN-udf-catalogue-1.0-20190925.html
	* Repo moved from volute to Github in early June: https://github.com/jontxu/udf-catalogue

Status.
Discussion about what examples for UDF has to be clarified.

MT: while it's in light-REC-page, it seems that modifying it with additions can take long being an EN, wrt SAMP wiki page solution or VEPs.

Pat: trying to envision how an ivo prefix are not a standardization.
optional features taken off the main ADQL specification.
Something for the TCG to take care of.

Jesus: a little ambigous having only the signature there. Implementations can differ.
Having an RDBMS specific implementation can help understanding the signature. Some healPix implementations based on pgSphere (Postgres).

3. DataLink templating
LM: RFC6570 - https://tools.ietf.org/html/rfc6570
MT: RFC6570 looks quite straightforward to implement. Possibly "level 3" to implement.
Not scared if this is te way to go.
FB: a simpler proposal 
PD: initially thought to go for "level 2", but agree that "level 3" is more complete.
"level 4" is about restricting value length and list- or associative-array-typed variables

FB+LM & Pierre F. proposal for templating (slides)
using LINK templating from VOTable A.1 appendix (non normative currently)

GD-F: Another good use case would be an attempt to drive an SIAv2 image search based on a catalog row containing separate ra and dec columns to use for the cone center.
In this case you have to construct a URL parameter string like “POS=CIRCLE 1.78 3.21 0.1” from those separate columns. (slide 8 answers this)

FB: wildcard substitution/incomplete strings in RFC6570? MT: doesn't seem so.
PD: not wildcard expansion, not different from simple solution, only fixing encoding details.
Also RFC emphasize the difference between the tempating and the actual URI you end up with.

GD-F: difference between DataLink service descriptor and the RFC templating of URLs.
The "simple" proposal helps keeping the semantics needs of DataLink (which we very much want to preserve) while RFC gives the templating solution.

MT: the two seem complementary each other.
Need for an element in the descriptor to link these two aspects.

FB: we need a mechanism to pick values from the table but also from the user, at the same time.

GD-F: This is very important to us as well.  I think a careful mash-up of RFC-6570 for the syntax and essentially the existing service-descriptor mechanism for the semantics of the substitutions would preserve this.

GD-F: I like the idea of using RFC-6570 for another reason: there is a chance of finding open-source implementations of this RFC in multiple languages.  We'll certainly care about at least Java and JavaScript and Python in our community.  For instance:
	* Python: https://github.com/python-hyper/uritemplate
	* JavaScript: https://www.npmjs.com/package/url-template