BonXai: Combining the simplicity of DTD with the expressiveness of XML Schema

Abstract

While the migration from DTD to XML Schema was driven by a need for increased expressivity and flexibility, the latter was also significantly more complex to use and understand. Whereas DTDs are characterized by their simplicity, XML Schema Definitions (XSDs) are notoriously difficult. In this paper, we introduce the XML specification language BonXai which possesses most features of XSDs, including its expressivity, while retaining the simplicity of DTDs. In brief, the latter is achieved by sacrificing the explicit use of types in favor of simple patterns expressing contexts for elements. The goal of BonXai is by no means to replace XML Schema, but rather to provide a simpler DTD-like alternative to schema designers that do not need the explicit use of types. Therefore, BonXai can be seen as a practical front-end for XML Schema. A particular strong point of BonXai is its solid foundation rooted in a decade of theoretical work around pattern-based schemas. We present in detail the formal model for BonXai and discuss translation algorithms to and from XML Schema.