A NIEM reference schema document (REF) is an authoritative definition schema document for a NIEM target namespace, therefore, all NIEM releases, core updates, and domain updates are composed of REFs and their associated namespaces. As a standalone artifact, REFs are always harmonized such that all types and properties are semantically unique, i.e., multiple versions of semantically identical types or properties do not exist within the documents. This page explains how REFs are integrated into a NIEM conformant document or package.
REFs are most easily specified through an XML Catalog. An XML catalog document is an instance XML document that describes a mapping between external entity references and locally-cached equivalents. It associates a URI reference with information about an external reference that appears in an XML document. An XML catalog document can be used to locate the replacement text for an external entity, or an alternate URI reference for a resource. Specifying a REF in an XML Catalog document is as follows:
name attribute of the uri element of the XML Catalog. Generally this is the URL of the schema document.uri attribute of the uri element of the XML Catalog. Generally this is a Unix style path to a file.name attribute specified in the XML Catalog of some uri element must exactly match the targetNamespace attribute of the named REF.<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN" "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd">
<catalog prefer="public" xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
<uri name="http://release.niem.gov/niem/appinfo/4.0/" uri="utility/appinfo/4.0/appinfo.xsd"/>
<uri name="http://release.niem.gov/niem/conformanceTargets/4.0/" uri="utility/conformanceTargets/4.0/conformanceTargets.xsd"/>
<uri name="http://release.niem.gov/niem/niem-core/4.0/" uri="niem-core/4.0/niem-core.xsd"/>
</catalog>