doubling down on VOEvent 2.0 (was Re: Draft VOEvent 2.1)

[Rob Seaman]

Howdy,

I changed the subject line to more closely resemble what has actually
been proposed.

Some of us have issued a draft note (mostly wordsmithed by Roy, but we
have signed off) which recommends layering VOEvent on JSON as a step to
supporting a binary serialization, probably Avro.

There are some long-discussed features desirable to LSST, such as
enhancing the portfolio concept into a more general container, including
image cut-outs.

Recent messages have also emphasized the significant need to retain
backwards compatibility to serve various ongoing VOEvent-layered
projects. After all, the main point of any transient alert messaging
from the point of view of LSST is to reach already deployed follow-up
facilities and archives (that is, precovery facilities).

It was inevitable that STC would become a talking point, and not just
because I, for one, talked about it. Addressing STC fully is a bigger
topic than VOEvent, or LSST, or IVOA, for that matter. I'm eager to find
out if some JSON or Avro related paradigm might offer schema tools
better than the poor pallid things provided by XML schema.

By all means let's revisit some of these longstanding design issues, but
let's do it with an eye to practicality. It is not obvious yet that any
changes to VOEvent 2.0 are needed. In particular, the current XML schema
that has been serving as a prototype for several years does not
implement all STC functionality that the highest priority LSST use cases
might need. A JSON or Avro based schema mechanism might permit enlarged
STC usage.

Perhaps later the XML schema could be updated to include such features.
I don't think this requires either a revision to the IVOA Recommendation
- or an errata. I have yet to here any features, other than related to
the binary serialization, that require any other changes to VOEvent 2.0.

Finally, it will be great if ZTF can be used as a pathfinder (for
VOEvent and other issues) to LSST. Engaging with the IVOA and other
communities (MPC springs to mind) early and often is one prerequisite to
success in that endeavor.

Rob Seaman
Lunar and Planetary Laboratory
University of Arizona