Design and Implementation of Highly Modular Schemas for XML: Customization of RuleML in Relax NG

Abstract

We present a re-conceptualization and re-engineering of the non-SWSL portion of the Derivation Rules subfamily of RuleML in the Relax NG Compact (RNC) schema syntax. The benefits arising from RNC schemas include decreased positional sensitivity and greater flexibility in modularization (from fine-grained modular to monolithic), as well as unification of human-readable (“Content Models”) and machine-readable (XSD/XML) versions. We introduce a Relax NG schema design pattern, enforced by RNC meta-schemas, that guarantees monotonicity (grammatical extension implies syntactic containment) when any of a large number of small expansion modules are merged. The original fifteen Derivation RuleML sublanguages are thus embedded in a syntactic lattice with hundreds of thousands of languages with semantics inherited from the top language. The original RuleML sublanguages are available through links, and customized languages are available through a GUI web-app. The GUI serves as the front end to a PHP-specified parameterized schema that takes a selection of customization options and returns a schema driver file. These options are encoded to facilitate determination of syntactic containment between any pair of languages. As in earlier (Derivation) RuleML language hierarchies, (logical) expressivity forms the backbone of the language lattice. The (parameterized) RNC schema serves as a pivot format from which XSD schemas, statistically-random XML test instances, monolithic simplified RNC content models, and HTML documentation are automatically generated. The RNC-based re-engineering of Derivation RuleML has already led to the discovery and patching of errata in RuleML versions 0.91 and 1.0, as well as to suggested enhancements of version 1.0 and a newly conceived version 1.1. The specifications of the RNC-based RuleML schemas are maintained at http://wiki.ruleml.org/index.php/Relax_NG .