Reuse of names and definitions

NIEM defines a methodology for broad communities to agree on:

  • The structure of data
  • Names for data
  • Value constraints on data

Every name, structure, and set of data constraints has a single authoritative representation, defined by a set of XML Schema documents. See for new and old NIEM releases. These schemas define base definitions, which can be refined, specialized, and extended, to define specific exchanges.

NIEM has distributed governance, meaning that different sets of data definitions are defined by different groups. This enables groups to focus on their areas of interest, with deliberate version control, and minimal conflict across different groups.

NIEM defines the following kinds of data components:

  • Simple types are the formats of unstructured values, like strings, numbers, and enumerations.

  • Complex types are the structure of objects. Each complex type defines a class of object (such as a person or vehicle), along with a list set of characteristics it has, or relationships that it participates in.

  • Elements describe uses of an object, or relationships that objects participate in, or characteristics of objects.

  • Attributes describe characteristics of objects, with values that are always simple types.

Each type of component has its own purpose, and each supports a different aspect of data, including JSON data and XML data. However, every NIEM data component has a few common characteristics:

  • A local name, which is a meaningful term that concisely identifies what a thing is, what it is for, and what it might hold. NIEM has a syntax for local names.

  • A definition, which is a descriptive statement that provides a detailed meaning for a thing. The criteria of what makes a good definition are identified in the NIEM Naming and Design Rules, section 7.4.

  • A namespace, which is a URL that acts as a universal identifier under which a set of data components are grouped. Each governance body, and each NIEM version, has unique namespaces that are assigned to it.

The qualified name of a data component is the namespace and local name together.

The reuse of these qualified names in exchange definitions, extensions, and messages allows the parts of the messages to be understood, and for similar components to be distinguished.

JSON, by itself, does not provide a mechanism for defining or using anything like XML namespaces. This is handled JSON-LD, which defines a way to use URIs for JSON keys, which works very similar to the way namespaces work.