The first production version of NIEM appeared in June 2006. It used Justice’s Global Justice XML Data Model as the foundation, but is being expanded to cover other common items relating to criminal justice and law enforcement.
Perhaps the major area of change is the unification of namespaces, a term applied to collections of tags.
The first version of NIEM had two main namespaces, Universal and Common.
Universal components were items that would be common to all parties using NIEM. Common components were items that existed in more than one domain.
If you are building software for the criminal justice market, write towards Universal and avoid Common where possible. It will make it easier to sell and install.