Games for Active XML Revisited

TL;DR

This paper explores rewriting mechanisms in Active XML using active context-free games, extending the framework to more expressive schemas and nested words, analyzing complexity and tractable cases for safe rewriting strategies.

Contribution

It introduces extensions to active context-free games for Active XML, including more expressive schemas and nested words, and analyzes the complexity and tractability of safe rewriting problems.

Findings

Rewriting on nested words increases complexity.

Safe rewriting problem is generally doubly exponential in complexity.

Identifies specific cases where the problem is tractable.

Abstract

The paper studies the rewriting mechanisms for intensional documents in the Active XML framework, abstracted in the form of active context-free games. The safe rewriting problem studied in this paper is to decide whether the first player, Juliet, has a winning strategy for a given game and (nested) word; this corresponds to a successful rewriting strategy for a given intensional document. The paper examines several extensions to active context-free games. The primary extension allows more expressive schemas (namely XML schemas and regular nested word languages) for both target and replacement languages and has the effect that games are played on nested words instead of (flat) words as in previous studies. Other extensions consider validation of input parameters of web services, and an alternative semantics based on insertion of service call results. In general, the complexity of the safe rewriting problem is highly intractable (doubly exponential time), but the paper identifies interesting tractable cases.