Is there any technical documentation available?

GJXDM has technical documentation and it explains the technical foundation behind the Global Justice XML Data Model and Dictionary. Its goal is to provide a solid infrastructure for storing and managing relationships between data entities independent of XML. These entities, and the relationships between them, are defined precisely and flexibly using two kinds of components: types and properties.

Reference link: https://www.niem.gov/technical/Pages/niem.aspx