Good approach to XSD schema versioning?

The company I am working for at the moment codify the schema or contract version into the root node. For example,

<PurchaseOrder_v1_2 xmlns="http://someNamespace">
...
</PurchaseOrder>

I am looking for people's opinions on this design ap开发者_如何学运维proach, as I am not convinced it is sound. For example, it requires that all services using this schema as a messaging contract are able to publish multiple versions to satisfy client requirements for different versions.

I would probably disagree with @hacktick's suggestion that versioning the namespace is conventional. I've never seen the W3C recommend that the namespace changes with version - certainly W3C namespaces don't do this - both versions of XSLT have the namespace http://www.w3.org/1999/XSL/Transform, for example.

Both encoding the version into the root and the namespace are changing the name of the element. In the case of the root, you are effectively stating that is an entirely different element with no defined relationship to the PurchaseOrder element in the previous version. In the case of the namespace change you are stating the same thing about *all the elements in the language.

Version attributes are more normal. May I suggest you read this thread on the XML-dev mailing list for some very well-informed discussion?

normally you versionize the url for the schema.

so you would have a schema called "schema" and you would then make reference to this like: "http://www.example.com/2011/01/schema" where 2011 and 01 are versions in the form of year and month. Example:
<PurchaseOrder xmlns="http://www.example.com/2011/01/schema">
</PurchaseOrder>

another approach is to use specify the version in the root element. if your root-element for example is called "PurchaseOrder" you would add an required version attribute (""). your version attribute would contain a simple number that increments with each version of your xsd. you must save a history of all your public xsds. this could lead to easier xsd urls but the extraction and the validation of these xml-files is a little bit harder.
Example:
<PurchaseOrder version="1" xmlns="http://www.example.com/schema"> </PurchaseOrder>

If you versionize the root element name ("PurchaseOrder_v1_2") you would have conversion problems in your xml-files if you go for another version.

Personally i would go for solution 1 (versionized namespaces). this is also recommended from the w3c. can't find a link for this statement though.