Abstract

The article 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 article 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 article examines several extensions of active context-free games. The primary extension allows for 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 values returned by the services. In general, the complexity of the safe rewriting problem is highly intractable (doubly exponential time), but the article identifies relevant tractable cases.

Highlights

  • Scientific contextThis paper contributes to the theoretical foundations of intensional documents, in the framework of Active XML [1]

  • We study the impact of the validation of input parameters for web service calls, and investigate an alternative semantics, where results of web service calls are inserted next to the node representing the web service, as opposed to replacing that node

  • We note that the results on flat strings in this paper do not directly follow from the results in [11], as [11] assumed target languages given by DFAs as opposed to deterministic regular expressions, which are integral to both document type definition (DTD) and more expressive XML schema languages

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Summary

Introduction

This paper contributes to the theoretical foundations of intensional documents, in the framework of Active XML [1]. The setting in [9] is as follows: an Active XML document is given, where some elements consist of functions representing web services that can be called. Necessary to reach a document in a given target schema (which could, for instance, require that the document contains at least one indoor event if the weather is rainy) Modelling this rewriting problem as a game follows the approach of dealing with uncertainty by playing a “game against nature”: We model the process intended to rewrite a given document into a target schema by performing function calls as a player (Juliet). As a basic intuition for the concept of replay, consider again the online news site example from Figure 1, and assume that the schema for the event service’s returns is (partially) given by @event_svc → (Sports|Movie)@event_svc, i.e. the event service allows for dynamic loading of additional results. As a side result of independent interest, we show that the word problem for alternating nested word automata is PSPACE-complete

Related work
Preliminaries
Games with regular target languages
Games with XML Schema target languages
Validation of parameters and Insertion
Validation of parameters
Insertion rules
Conclusion
Full Text
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