An XML catalog is a XML document that assigns locations to files. This can be used to override the file locations assigned by NIEM XML schema import statements without having to modify the original schema itself.
XML catalogs are an OASIS standard.
While XML catalogs provide a broader set of features that may be used as needed by developers and implementers for namespace resolution, the primary ways that NIEM uses XML Catalogs for releases are presented here.
A XML catalog has a root-level catalog element. NIEM releases use uri elements under the catalog element to associate namespaces with file locations. A subset of the XML Catalog file from the 4.0 release, xml-catalog.xml, is shown below.
name attribute holds the target namespace of the XML schema fileuri attribute holds the absolute or relative file location<?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/3.0/" uri="utility/conformanceTargets/3.0/conformanceTargets.xsd"/>
<uri name="http://release.niem.gov/niem/niem-core/4.0/" uri="niem-core/4.0/niem-core.xsd"/>
</catalog>
The template below may be used as a starting point for creating an XML catalog:
<?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="" uri=""/>
</catalog>
In addition to mapping target namespaces of XML schemas to file locations, XML catalogs can also be used to map a CSV Code List file to a source identifier.
The example catalog below maps:
- the target namespace of the NIEM Core 4.0 schema to a relative file location.
- the source identifier for GENC 3-7 3-character country codes to a relative file location for the CSV file.
<?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/niem-core/4.0/" uri="niem-core/4.0/niem-core.xsd"/>
<uri name="http://api.nsgreg.nga.mil/geo-political/GENC/3/3-7" uri="codes/genc/geo-political/3-7/genc_geo-political_3-7_char3.csv"/>
</catalog>
XML Catalogs are supported by many common XML tools, such as Oxygen XML Editor, XMLSpy, and Xerces. See the following for more information about XML catalogs.