RELAX NG Converter is a tool to convert schemas written in various schema languages to their equivalent in RELAX NG.
It supports schemas written in XML DTD, RELAX Core, RELAX namespace, TREX, W3C XML Schema, and RELAX NG itself.
This release includes software developed by the Apache Software Foundation (https://www.apache.org/).
To convert a schema written in either RELAX Core, RELAX namespace, TREX, or W3C XML Schema, enter the following:
java -jar rngconv.jar myschema.xsd > result.rng
The converter detects the schema language automatically (except for XML DTDs) and writes the result to "result.rng".
To convert an XML DTD, enter the following:
java -jar rngconv.jar -dtd myschema.dtd > result.rng
Note that you need the -dtd option.
Please find the complete documentation here!