The NIEM Technical Architecture Committee (NTAC) is in the process of developing guidelines and specifications supporting the use of JSON with NIEM.
JSON is defined by RFC 4627:
The NTAC has produced Non-Normative Guidance in Using NIEM with JSON. The guidance lays out how a NIEM IEPD describes a JSON message, by showing that XML elements, attributes, and other features can be expressed as JSON objects. These guidelines use JSON-LD, which supports namespace-qualified names, maintains the RDF conceptual model used by NIEM, and supports widely-used linked data methodologies.
As part of the NIEM 4.0 release, NIEM has published online a NIEM JSON-LD context, to provide a Uniform Resource Identifier (URI) mapping for each namespace used in NIEM. This enables JSON users an easy way for JSON messages to use and reference the model, providing an easy-to-use linked data approach to NIEM.
Future work will develop specifications supporting the use of NIEM JSON messages as a fully NIEM-conformant representation of a NIEM IEPD. In addition, work may include tools that support the transformation of data between NIEM JSON and NIEM XML.