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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: XML Schemas: Best Practices ? Versioning
 Actually, option 1 and 1.5 aren't alternatives, they are two parts of one
solution. When you have the case 2 (the namespace really hasn't changed,
the corresponding schema has been extended). you actually need both parts.
Adding the version attribute into the instance document allows the instance
generator/author to declare the earliest version that the instance
document is compatible with. The version attribute within the schema could
be used to declare the version of the schema.
This
pattern can be seen within XSLT and SVG where there is a "version" attribute on
the <xsl:transform> or <svg:svg> element to indicate what version of
XSLT or SVG is in use. At this time, there is only one legal value for
version for these namespaces, however it implies that future versions of XSLT
and SVG may keep the same namespace but add new values for the version
attribute. Current v1 processors are required to fail when presented with
a later version attribute, however some tools (like an XSLT documentation tool)
much think that it is reasonable to process just what it recognizes of a v2
document.
For
greatest interoperability, you would only want to specify version="2.0" if you
were using some version 2.0 features in your document and use version="1.0"
otherwise.
In the
case where you are making breaking changes to a definition, you have no choice
but to use a distinct namespace at least for the breaking changes.
For example, if SVG 2 decided the interpretation of <rect> needed to
change, but everything else in SVG 2 was upward compatible with SVG 1, there
could be a new namespace just for <rect>:
<svg xmlns=http://www.w3.org/2000/svg version="2.0"
xmlns:svg2="http://www.example.org/bogusuri">
<!-- svg 1.0 rect, draws a
rectangle -->
<rect x="10" y="20" width="20"
height="20"/>
<!-- svg 2.0 rect, draws
rectanglasaurus -->
<svg2:rect x="10" y="20" width="30"
height="20"/>
</svg>
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