VOEvent draft specification 0.3

[Roy Williams]

Welcome to the VOEvent Working Group mailing list, and thank you for taking part.

Mail to this list is archived at http://www.ivoa.net/forum/voevent/ and there is a Twiki 
page that will act as the web page for the WG, at 
http://www.ivoa.net/twiki/bin/view/IVOA/IvoaVOEvent.

The draft specification of VOEvent is at
http://www.ivoa.net/internal/IVOA/IvoaVOEvent/VOEvent-0.3.htm

So what are we trying to achieve?

There are several projects coming online that will discover immediate events in the sky, 
for example Swift, Ligo, Pannstars, Palomar-Quest, and LSST. There are also many new 
robotic telescopes that will follow-up such events very quickly. In the past, several 
"human-centric" event systems have been very successful, for example the IAU telegrams, 
the Gamma-ray burst Coordinate Network, the Astronomer's Telegram, etc. These systems use 
natural-language text to describe the nature of the event, and send all qualified events 
to all subscribers.

However, we expect a larger number of events as the new projects come online, and we 
expect them to be handled by machines. We expect subscribers to make a careful filter for 
the events they want, for example events from a specific survey, events that will be above 
the horizon. There could be very detailed subscription requirements, perhaps events where 
the R-band magnitude increase was at least 2. Machines can select events based on 
coincidence. A gravitational wave detector, for example, might produce a large number of 
candidate events, but the interesting ones coincide with candidates from another detector. 
Further, the interoperability that we propose here will allow event federation: for 
example finding coincidence events between Swift and Ligo.

To enable this more sophisticated processing, we should
(1) Build a more structured message that is accessible to machines, and
(2) Create a uniform citation system for event messages, and
(3) Separate message structure from transport

To illustrate (1), the position of an event in the sky, for example, should be defined 
formally in the VOEvent packet instead of being part of a text descriptions -- and 
therefore inaccessible to a machine. For (3), we need not rely on email for moving VOEvent 
messages, but other protocols would be more useful for machines, perhaps web services.

There is no intention here of destroying existing systems, but rather achieving the goals 
described above with minimal re-engineering. At this point, we are interested only in (1) 
above: reaching international agreement on the semantic content of an event message. This 
will form the basis of a valuable interoperability.

Over the last few weeks, a small group of us (Bloom, Graham, Plante, Stoughton, Williams, 
Wozniak) have been drafting a document that starts this semantics of a structured VOEvent. 
The draft specification is at
http://www.ivoa.net/internal/IVOA/IvoaVOEvent/VOEvent-0.3.htm

Please take a look and render your comments to this group. (If you would like to edit the 
document directly, please us strikethrough (<s> ... </s>) to delete, and font color (<font 
color="red"> .... </font>) to add new text. Please also note your changes in the change 
history at the end.

Specific questions:

-- What other astrophysical event-reporting systems are out there that we have not 
mentioned in the document?

-- We call for additional schemas to represent "instrument configuration" and "event 
description". The RTML project provides the former for optical telescopes: what other 
schemas should be incorporated in these roles?

-- Can events from existing systems be represented (in principle) by the draft semantics?

-- Is it reasonable to have a single "importance" number (section 3.6) between 0 and 1 
that expresses "something" about the importance of the event?

-- We have the basic type of an event chosen from the list: discovery, followup, 
intendedFollowup, merge, veto, reject (section 3.1). Are these the right types?

-- Existing systems characterize events by their astrophysics, for example the IAU 
telegram uses this list: Comets, Supernovae, Novae, Outbursts Of Unusual Variable Stars, 
Features On Planetary Surfaces. How can we (should we?) settle on an event description 
like this?

-- Should we specify event time by Julian day number? Is this unambiguous and universal?

-- When we specify sky position, is it reasonable to expect J2000 coordinates with error 
box  that may be disk, ellipse, or polygon?

-- Two existing systems have definitions of "event type", including Comet, Microlensing, 
etc etc (see sections 5.1 and 5.3). Can we make a comprehensive list of such "event types" 
for submitters to select from?

Thank You
Roy Williams

--------
California Institute of Technology
roy at caltech.edu
626 395 3670