A posting from Henry S. Thompson (HCRC Language Technology Group, University of Edinburgh) announces the availability of XSV Version 1.3. XSV (Validator for XML Schema) is an open source (GPLed) work-in-progress attempt at a conformant schema-aware processor, as defined by the W3C Recommendation for XML Schema. A significant change has been introduced in version 1.3, which "switches from using DTD to pre-validate schema documents to using schema-for-schemas. Hitherto, XSV has pre-validated all schema documents involved in a schema-validation episode with the DTD for schemas. This was both not quite right, in that it meant certain constraints were not enforced, because not expressed in the DTD, and messy, in that if a schema document included an internal subset, it was tricky to preserve it. With the advent of version 1.3, all schema documents are now pre-validated with a pre-compiled version of the schema for schemas itself. Even if a DOCTYPE is present, XML 1.0 validation will not be performed, although processing will reflect attribute defaults and general entity bindings, as required by XML 1.0." The authors have done their best with regression testing to ensure that the new XSV release is working properly, but there is potential for introduction of new vulnerabilities and backwards incompatibilities; feedback from the public is solicited. Both the online web version and the standalone/download implementation of XSV have been upgraded to XSV version 1.3. The XSV Schema validator has been developed by Henry S. Thompson and Richard Tobin, with contributions (Web interface) by Dan Connolly.

The version of XSV under active development will validate XML schema documents with the namespace URI http://www.w3.org/2001/XMLSchema. The online/web form-based interface supports validation using one of two forms: (1) one for checking a schema which is accessible via the Web, and/or schema-validating an instance with a schema of your own; (2) another if you are behind a firewall, or have a schema to check which is not accessible via the Web. The default output is text/xml with an XSLT stylesheet; one may select other fallback output formats for browsers which don't support http://www.w3.org/1999/XSL/Transform XSLT stylesheets. XSV has been developed at the Language Technology Group of the Human Communication Research Centre in the Division of Informatics at the University of Edinburgh, with support for one of the developers (Henry Thompson) from the World Wide Web Consortium. As documented in the status report, most features of XML Schema relevant to validation have been implemented, at least in part. Features said not to be implemented yet include: "(1) Simple type conformance, other than enumerations and max/min for numeric types; (2) Detailed enforcement of derivation by restriction; (3) Redefinition of named groups and attribute groups; (4) Occurrence ranges over 100 for elements or groups in content models -- a performance limitation."