Summary: features for VOEvent v2.0

[Matthew Graham]

Hi Rob,

On Apr 9, 2010, at 2:41 PM, Rob Seaman wrote:

> The general goal is to retain backwards compatibility to v1.1. 

I'd like to ruminate on this for a moment. I'm assuming that backwards compatibility here means that a VOEvent 2.0 client can handle a VOEvent 1.1 packet, i.e. a client designed specifically for VOEvent 2.0 will encounter no problems if presented with a VOEvent 1.1 without any special provision for it (no "if version = 1.1 then" statements). Now any VOEvent packet is defined according to a particular version of the schema, enshrined in the namespace to which the packet belongs. So the VOEvent 1.1 packet:

<voe:VOEvent>...

and the VOEvent 2.0 packet:

<voe:VOEvent>...

will have different namespace attached to the 'voe' prefix. Any piece of software which makes use of the namespace - XPath and XQuery, package names in generated code from the schema, etc. - will therefore break when presented with a packet from a different namespace, especially if it is built just from the 2.0 spec. Note this is not about validating the packet against the schema, this is about parsing the packet. The exact same situation exists between VOSpace 1.0 and 1.1 because you are defining a versioned message protocol and code written to work with one version will not automatically work with the other.
If you want your code to work with both versions of  VOEvent then you will have to specifically write it to deal with VOEvent 1.1 and VOEvent 2.0.

	Cheers,

	Matthew


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