NIEM JSON documents are expressed using JSON-LD, a method of using JSON to express linked data, including Resource Description Framework (RDF) and Web Ontology Language (OWL) data. There are tools available that transform JSON-LD data in various ways.
JSON-LD is a pattern of using JSON that maps to RDF. NIEM has a mapping to RDF, as described by the NIEM Naming and Design Rules, section 5, The NIEM conceptual model. The expression of NIEM data in JSON-LD is, basically, the JSON-LD form of the RDF data that NIEM XML data would represent.
For most people, that’s too much information, and it’s sufficient to know that NIEM JSON data follows the structure and names of NIEM XML data.
JSON-LD allows a message to use short names as object keys, but still have those
keys represent full URIs, which can represent the qualified names used in NIEM
XML. The short names can have used XML qualified name syntax (e.g.,
nc:Vehicle), or can have a short syntax defined by an exchange developer
(e.g., vehicle). These names are specified by a JSON-LD context,
which is a JSON document (or part of a JSON-LD document).
JSON-LD provides a simple way of expressing the identifier of an object, using a
construct called @id. These identifiers handle the identification and
referencing that are handled by NIEM’s structures:id, structures:ref, and
structures:uri attributes.