Newbie question : how to specify a source instrument in a VOEvent ?

[Le Fèvre Jean-Paul]

Hi,

We have just started a discussion about how to format VOEvents for the Svom mission. (A future French-Chinese space mission dedicated to GRB). 
There will be at least 5 instruments involved in the mission capable of generating data. My question is the following :

What is  the best way to specifiy in a VOEvent packet which  instrument is the source of data  ?

- a token in the localID of the IVORN (Fermi and Swift seem to have chosen this solution),
- using a <Group> element with a different name attribute for the different instruments,
- the <How> element referencing a rtml document describing the different instruments,
-  other.

It is not clear for me which solution is the best, so I need advice !
Thank you in advance for your help,

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Jean-Paul Le Fèvre 
Svom FSC project manager - CEA Saclay Irfu
Mél :  jean-paul.lefevre at cea.fr
Tél : +33 1 69 08 34 58