VOEvent - Param comment

[Alasdair Allan]

Tony Linde wrote:
> The reason that VOEvent and VOTable has stuff like <param> tags and  
> the like (and VOTable has a lot worse) is because they are dead-end  
> technologies.

Funnily enough, I'm going to disagree with you Tony. But you sort of  
knew I would...

> They cannot be used for anything except being looked at by humans  
> (possibly mediated by pretty graphics).

They're being used right now by software to do autonomous follow-up,  
and the software is making decision partially based on the contents  
of those <Param> tags.

> If they were used in downstream applications (by people other than  
> those creating the standards)...

I create the OGLE messages, they aren't being used just by me  
anymore, and decisions to observe are made at least partially, on the  
<Param> tags they contain. Robert and I discussed a "canonical"  
translation of the GCN when I was out at LANL, and hopefully that'll  
get written up at some point. Once documented by the provider the  
<Param> tags are useful to software, how exactly is that different  
from documenting them in a schema. You still have to write the  
software with knowledge of how to interpret the schema in an  
astronomical context, me knowing that <trigger_num> is a integer  
(about all the schema could tell a downstream autonomous client)  
doesn't really help very much over a <Param> where it's a string. The  
downstream code still needs to have inbuilt knowledge of what to do  
with the semantic content once it has been extracted from the messages.

> they would cause errors and failures and would return false data  
> and so would not have come into existence or would have been  
> replaced before getting ratified.

I think what we disagree about is where the documentation should be,  
you and others in the VO seem to be arguing that the schema is the  
documentation, and that it defines the standards. I and others, some  
in the VO and some outside, argue that for (for instance) a lot of  
scientific programmers who came from non-CS backgrounds, the standard  
is the document which describes the standard. If the schema disagrees  
with the documented standard, it's the schema that is in the wrong.

If you accept my world view as correct, and that's an excellent idea  
surely? Then it doesn't matter if the description what a <Group> of  
<Param> tags represents is defined in a document somewhere else,  
somewhere else that might not be related to the IVOA at all. In fact  
I think our difference is actually not about semantics at all but a  
classic peer-to-peer vs. hierarchical debate.

The VOEvent group has deliberately set out to create a standard  
without central control, providers and consumers can appear and  
disappear without application to a central authority, and without a  
formal process. We thought that was necessary, both for the initial  
adoption, and for continued use. While a great service which has  
served to astronomy community well, and will continue to do so,  the  
flaws of the GCN architecture are very evident to all of us working  
in the robotic telescope community. The flaws have nothing to do with  
the use, or not, of XML.

Going down the creation of schema for individual message types route  
you would not, under any circumstances, just have had the adoption of  
VOEvent by the HTN community. The VOEvent group wants to make sure  
that it isn't just huge projects, that can afford to employ numerous  
dedicated programmers, that can author and consume event messages.  
Science is about serendipity, at least the fun exciting bits are, not  
about central planning.

Al.