Writing an XSLT optimizer in XSLT

In principle, XSLT is ideally suited to the task of writing an XSLT or XQuery optimizer. After all, optimizers consist of a set of rules for rewriting a tree representation of the query or stylesheet, and XSLT is specifically designed as a language for rule-based tree rewriting. The paper illustrates how the abstract syntax tree representing a query or stylesheet can be expressed as an XML data structure making it amenable to XSLT processing, and shows how a selection of rewrites can be programmed in XSLT. The key question determining whether the approach is viable in practice is performance. Some simple measurements suffice to demonstrate that there is a significant performance penalty, but not an insurmountable one: further work is needed to see whether it can be reduced to an acceptable level.