such as roles, associations, and augmentation from industry standards, such as the World Wide Web Consortium (W3C) XML Schema language. NIEM schemas The NIEM reference schemas are a set of interrelated schemas that define NIEM data components. Each schema defines its own target namespace. Schemas in the reference set may import one another by namespace in order to use (or reuse) components they define. In general, domain reference schemas import schemas from the Core. The NIEM reference schema set represents the full set of data components in NIEM. The following kinds of XML schemas are associated with the NIEM architecture: NIEM reference schemas: Schemas containing content created or approved by the NIEM steering committees are periodically released in schema distributions. Subset Schema: a NIEM-conformant schema, containing only the parts of the reference schemas needed to support a particular exchange. Support schemas: NIEM includes three special schemas, appinfo, structures and proxy, for annotating and structuring NIEM-conformant schemas. Extension Schema: a NIEM-conformant schema which adds domain- or application-specific content to the base NIEM model. Exchange Schema: a NIEM-conformant schema which specifies a document in a particular exchange. Constraint Schema: a NIEM-conformant schema which adds additional constraints to NIEM-conformant instances, but which is assumed to validate in concert with existing NIEM-conformant or subset schemas. A constraint schema need not validate constraints that are applied by other schemas. Codelist Schemas: a NIEM-conformant schema which provides a list of acceptable values that a data element will be constrained to. The only mandatory schemas for validation are the NIEM reference schemas or a correct subset, however the IEPD specification requires that an IEPD include an exchange schema (along with the reference schemas or subsets) to be considered a complete IEPD. The NIEM schemas may import additional schemas, such as code table schemas, as needed. An optional extension schema may be used to add extended types and properties for components not contained in NIEM, but which are needed for the exchange. NIEM Naming and Design Rules (NDR) The naming and design rules for NIEM are documented in the NIEM NDR, which specifies the data model, XML components, and XML data for use with NIEM and provides a basis for NIEM conformance. The current version is NDR v5.0, which was released on December 18, 2020. NIEM is based on several concepts from the International Organization for Standardization (ISO) 11179, which provides guidelines for the naming and definition of