A open source multi-format schema converter based on RELAX NG. Includes documentation and download.

Uses instance documents as a lightweight schema language; sample documents are marked up with the information needed to guide a validator.

Paper by Dongwon Lee and Wesley W. Chu comparing XML DTD, XML Schema, XDR, SOX, Schematron, and DSD.

Specification of a framework for modular validation of XML documents.

integrity management of distributed XML data. Provides a validation rules language and processing engine that allows constraints beyond schema and DTD validation.

Automated data quality checking of XML content.

Checks an XML document (specified by URL) for well-formedness and optionally DTD-based validity and namespace correctness. Outputs canonical XML. Runs over the web and can be downloaded.