Thanks for your reply. I found out the the database connection is ok and it is working as defined.
My fault was that I defined in my pesistence.xml the jta-data-source with
<jta-data-source>jdbc/workflow-db</jta-data-source>
but the prafix "java:/" is necessary for jboss (?). After I changed the jta-data-source tag to:
<jta-data-source>java:/jdbc/workflow-db</jta-data-source>
the application works well and all tables in my database were generated correctly.
This is confusing because on a Glassfish Server the jta-data-source is always declared without the prafix "java:/" . So it seems to me that the persistence.xml configuration is depending on the app-server platform :-/