In particular, could you compare in detail this relaxng method and the
similar xml schema approach using substitution groups and abstract
schema types? (note that the substitution group part of this is
unnecessary but results in easier to read xml)? After studying your
blog post I don't see any major differences between the relaxng
approach and the xml schema approach beyond the differences between
relaxng and xmlschema. On the other hand this is the first time I've
seen relaxng.
Are there any tools like jaxb that work with relaxng?
thanks
david jencks
On May 21, 2008, at 10:56 AM, Jason van Zyl wrote:
Bryon,
How would you compare this with a method like this using XML Schema.
I'm not a huge fan of XSD, but there is a lot of tooling for XSD
especially in IDEs and that would be something we have to consider.
Do you actually use this method you describe in a production system,
or just a thought experiment?
On 18-May-08, at 2:49 PM, Bryon Jacob wrote:
I wrote a kinda lengthy blog post about doing this sort of thing:
http://freedomandbeer.com/posts/extensible-xml-with-xml-namespaces-and-relaxng
RelaxNG is a fantastic language for specifying schemas for XML -
the grammar notation is very natural to write in. Allowed elements
are specified using "name classes", and you can perform set
arithmetic over those classes to achieve some amazing results for
extensibility, by delegating validation of extension elements to
the author of the extensions, while retaining the ability to assert
the validity of the core document structure.
If I understand the problem that you're trying to solve here, it is
exactly analogous to the example in my blog post. I think you
would probably structure your xml somewhat differently than below -
you define the "profile" namespace prefix on the <extension>
element, but since the profile isn't a child of that element, the
declaration doesn't carry through. For your goals here, I don't
even think the <extension> element buys you anything -- what you
really want to do, it seems, is change the core Maven schema to
allow arbitrary extensions to a project's XML, as long as they are
partitioned into a new namespace - rewriting your example XML:
<project xmlns="http://maven.apache.org/POM/4.0.0";>
...
<profile xmlns:profile="http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
">
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<profile:deactivation>
<profile:os>
<profile:name>Windows 98</profile:name>
<profile:os>
</profile:deactivation>
</profile>
...
</project>
Using RelaxNG, you could write the rule for the <profile> element
to allow any element NOT in the maven namespace to be included:
PROFILE =
element maven:profile {
element maven:activation {
element maven:activeByDefault { xsd:boolean}
}
| ANY_EXT_ELEMENT*
}
ANY_EXT_ELEMENT =
element * - maven:* {
attribute * { text }*,
( text* & ANY_EXT_ELEMENT* )*
}
And then, you could declare a RelaxNG grammar to parse a "project
with profile enancements" document like:
include "maven.rnc" {
ANY_EXT_ELEMENT =
element * - (maven:* | profile:*) {
attribute * { text }*,
( text* & ANY_EXT_ELEMENT* )*
}
| DEACTIVATION
}
DEACTIVATION =
element profile:deactivation {
element profile:os {
element profile:name { text }
}
}
Like I said, there's a much more detailed, and analogous, example
at the link above. hope this helps!
- Bryon
On May 16, 2008, at 1:53 PM, nicolas de loof wrote:
Hello,
many thread on this list makes proposal for some changes in the
POM.xml
format, to be included in 4.1.0 modelVersion.
Could we use XML namespaces to support progressive enhancements ?
Based on
this, proposal for new features could be added to maven, using an
<extension> to support the new schema, without requirement to wait
for next
major version to include POM structure changes.
example : considering the recent proposal for profiles enhancements
http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
<profile>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<deactivation>
<os>
<name>Windows 98</name>
</os>
</deactivation>
</profile>
Could be rewritten :
<extensions>
<extension xmlns:profile=
http://docs.codehaus.org/display/MAVENUSER/Improvements+to+Profile+Activation+Deactivation
<groupId>org.apache.maven.proposals</groupId>
<artifactId>profile-enhancements</artifactId>
</extension>
<extensions>
<profile>
<activation>
<activeByDefault>true</activeByDefault>
</activation>
<profile:deactivation>
<profile:os>
<profile:name>Windows 98</profile:name>
</profile:os>
</profile:deactivation>
</profile>
This can be compared with namespace support in Springframework
context files
: adding a new custom namespace allow to make the configuration
less verbose
or more powerfull, with no requirement to change the base XML model.
Nicolas
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Thanks,
Jason
----------------------------------------------------------
Jason van Zyl
Founder, Apache Maven
jason at sonatype dot com
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What matters is not ideas, but the people who have them. Good people
can fix bad ideas, but good ideas can't save bad people.
-- Paul Graham
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