Are different versions of the same event unique?

[Matthew Graham]

Hi,

An issue has come up with Scott Barthelmy's GCN/TAN VOEvent distribution that he would like to see resolved by this group. Notifications of the same astronomical event need to be sent out in both VOEvent 1.1 and VOEvent 2.0 forms (just accept the premise and don't question it) - should these have the same identifier or different ones? The information content in both is the same - the events are identical except for such changes as required to comply with the different schema. Currently Scott is sending out events with different IVORNs:

<?xml version = '1.0' encoding = 'UTF-8'?>
<voe:VOEvent
     ivorn="ivo://nasa.gsfc.gcn/SWIFT#FOM_Obs_34073224-501"
     role="observation" version="1.1"
     xmlns:voe="http://www.ivoa.net/xml/VOEvent/v1.1"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:xlink="http://www.w3.org/1999/xlink"
     xsi:schemaLocation="http://www.ivoa.net/xml/VOEvent/v1.1 http://www.ivoa.net/xml/VOEvent/VOEvent-v1.1.xsd" >
 <Who>
   <AuthorIVORN>ivo://nasa.gsfc.tan/gcn</AuthorIVORN>


<?xml version = '1.0' encoding = 'UTF-8'?>
<voe:VOEvent
     ivorn="ivo://nasa.gsfc.gcn/SWIFT#FOM_Obs_34073224-502"
     role="observation" version="2.0"
     xmlns:voe="http://www.ivoa.net/xml/VOEvent/v2.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://www.ivoa.net/xml/VOEvent/v2.0  http://www.ivoa.net/xml/VOEvent/VOEvent-v2.0.xsd" >
 <Who>
   <AuthorIVORN>ivo://nasa.gsfc.tan/gcn</AuthorIVORN>
   <Author>

but subscribers and brokers are going to have to check for coincidences since these are reporting the same astronomical event from the same source (note that the same event from different independent sources, e.g., CRTS and PTF, would have different IVORNs). So should different serializations of the same event carry different identifiers?
Could they cite each other to prevent confusion?

	Cheers,

	Matthew
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