This file, part of Hibernate code: https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/boot/cfgxml/internal/JaxbCfgProcessor.java
references this URI on line 51, but it's a dead link
public static final String HIBERNATE_CONFIGURATION_URI = "http://www.hibernate.org/xsd/orm/cfg";