RELAX NG (ISO/IEC 19757-2) is an International Standard schema language for XML. A RELAX NG schema specifies a grammar that a validator can apply to XML documents to determine whether or not they are schema-valid.
RELAX NG is a schema language for XML. A RELAX NG schema specifies a grammar that a validator can apply to XML documents to determine whether or not they are valid.
RELAX NG was invented by James Clark and MURATA Makoto and standardized first at OASIS and subsequently in ISO/IEC JTC 1 as an International Standard, ISO/IEC 19757-2 (available here). It is formally expressed with a strong mathematical basis.
Some features of RELAX NG:
Schemas can be expressed using either XML, or a non-XML "compact syntax".
Support for pluggable datatype libraries. (Most validators come with support for the datatypes defined by W3C XML Schema.)
Ability to specify the start (root) elements for documents.
Slightly more sophisticated grammar modelling that that permitted by XML DTDs or W3C XML Schema.
Although enjoying less market share than W3C XML Schema, RELAX NG is popular among markup experts and is used as the schema language of other standards such as ODF, MathML and EPUB.
RELAX NG schemas can be programmatically converted to XML DTDs or W3C XML Schemas using James Clark's free and open source trang utility.
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