[mdr-users] Using transient storage

I'm using Netbeans MDR to transform a proprietary model format to UML 
XMI (standalone). In every run of the transformation, I want to build 
the model from scratch, export it, and throw the repository away 
afterwards. That's why I thought that ...memoryimpl.StorageFactoryImpl 
would be the storage implementation to use.
A single export works fine, but when exporting twice I run into 
exceptions. The same exceptions can be produced by the piece of source 
code below.
 From a quick look at ...mdr.persistence.memoryimpl.StorageImpl, I 
thought that not assigning STORAGE_ID values would lead to independent 
repositories.


public static void main( String[] args ) throws Exception
{
   Map properties = new HashMap();
   properties.put(
     "storage",
     "org.netbeans.mdr.persistence.memoryimpl.StorageFactoryImpl"
   );
   // I'm not setting the STORAGE_ID.
   // properties.put( StorageFactoryImpl.STORAGE_ID, ... );

   MDRepository firstRepository = new NBMDRepositoryImpl( properties );
   System.out.println(
     "firstRepository extents: "+
     Arrays.asList( firstRepository.getExtentNames() )
   );
   MDRepository secondRepository = new NBMDRepositoryImpl( properties );
   // following line throws exception:
   System.out.println(
     "secondRepository extents: "+
     Arrays.asList( secondRepository.getExtentNames() )
   );
}

The stack trace of the exception is:
org.netbeans.mdr.util.DebugException: Missing storage files or different 
storage version.
   at ...storagemodel.MdrStorage.initializeIndexes(MdrStorage.java:507)
   at ...storagemodel.MdrStorage.rollback(MdrStorage.java:554)
   at ...util.TransactionMutex.end(TransactionMutex.java:73)
   at ...util.MultipleReadersMutex.leave(MultipleReadersMutex.java:173)
   at ...NBMDRepositoryImpl.endTrans(NBMDRepositoryImpl.java:249)
   at ...NBMDRepositoryImpl.boot(NBMDRepositoryImpl.java:1331)
   at ...NBMDRepositoryImpl.initCheck(NBMDRepositoryImpl.java:758)
   at ...NBMDRepositoryImpl.getExtentNames(NBMDRepositoryImpl.java:347)
   at Main.main(Main.java:58) /* ="secondRepository.getExtentNames()" */


Can anybody tell me what I'm doing wrong?

Thanks in advance,
Frank