[infinispan-dev] XML namespaces in configuration files

[Vladimir Blagojevic]

Hey all,

After consultation with Alexey I think the following emerges as the best approach for management of xml schemas, configuration pojos and configuration file backward compatibility. 

We should remove references to schema version in namespace and we might even rename namespace to something like "http://infinispan.org/xml/ns/ispn" and use a prefix "ispn" rather than tns. We could roll this in 4.1 final release. We leave 4.0 schemas as is, but 4.1 signifies a break and a new schema name-spacing that we intend to keep. How do we treat customer who want to use their 4.0 configuration files in 4.1? We tell them to remove references to old namespace from their configuration files. Thanks to ISPN-431 they are not affected. 

Since we removed references to configuration version in schema, as far as our configuration beans go, we are fine as long as we add properties to elements and even adding new configuration elements in ok.  In essence, we are fine as long as we do not remove/rename existing attributes and elements from our configuration pojos. Adding new elements to configuration will still work. For example, lets say that 5.0 adds some configuration elements regarding JPA. Reading 4.1 configuration file in 5.0 is ok since we kept all those elements from 4.1 in 5.0, and for JPA element default configuration settings are initialized anyway. 

Let me know what you guys think.

Vladimir
 


On 2010-05-11, at 5:43 PM, Alexey Loubyansky wrote:

> Hi Vladimir,
> 
> yes, that's tricky. I can't say we have an elegant solution for that.
> 
> I can't tell you what we do wrt EJB metadata (ejb-jar.xml/jboss.xml) as an example.
> For jboss.xml we have common JBossMetaData.
> http://anonsvn.jboss.org/repos/jbossas/projects/metadata/ejb/trunk/src/main/java/org/jboss/metadata/ejb/jboss/JBossMetaData.java
> 
> It contains binding annotations but w/o the schema-level ones such namespace, etc. Then per schema version we create a top level class, e.g.
> http://anonsvn.jboss.org/repos/jbossas/projects/metadata/ejb/trunk/src/main/java/org/jboss/metadata/ejb/jboss/JBoss50MetaData.java
> http://anonsvn.jboss.org/repos/jbossas/projects/metadata/ejb/trunk/src/main/java/org/jboss/metadata/ejb/jboss/JBoss51MetaData.java
> 
> There we specify the namespace and which properties we want to bind. So, actually, for some schemas common JBossMetaData contains more metadata than it is available in those schemas but those properties are just not bound for those schema versions. But the deployers regardless of the deployment descriptor version deployed use the same JBossMetaData API.
> In this case, though, it's only for the top-level class (root element). Although, we could have some tricks for other classes/elements as well.
> 
> Other metadata (sub)projects (web, ear, rar, etc) use the same approach. (There are also tests for consistency between XSD/DTD and Java bindings, i.e. structural equivalence)
> 
> What is a bit different, we don't include schema version in the namespace. Schema versions are different but the namespace stays the same. The same is true for JEE spec schemas.
> But even if we did, the current approach would still work.
> 
> If you have some tricky cases/requirements then let's discuss them on the forums. It might be relevant to other projects as well.
> 
> Best regards,
> Alexey
> 
> On 5/11/2010 9:46 PM, Vladimir Blagojevic wrote:
>> Hi Alexey,
>> 
>> Need an advice regarding best practices when it comes to XML schema management and references in configuration files. In infinispan project we have used JAXB annotated classes to annotate configuration pojos, automate manage configuration loading, and do schema creation. We have used the package-info.java files annotated with JAXB annotations to declare schema namespaces[1]. Then in turn we have generated XML schema file using JAXBContext#generateSchema.
>> 
>> The current namespace is urn:infinispan:config:4.0, but this will change to urn:infinispan:config:4.1, urn:infinispan:config:5.0, etc in the future. What are our options for configuration file backward-compatibility?
>> 
>> Best regards,
>> Vladimir
>> 
>> 
>> 
>> [1] http://fisheye.jboss.org/browse/Infinispan/trunk/core/src/main/java/org/infinispan/eviction/package-info.java?r=619