Positive Active XML ∗

XML is a data model and representation format for semi-structured data. It is becoming the standard for data exchange between web-applications. The access to XML data is facilitated by Web Services, programs over the web that take XML parameters and returning XML results. The increasing popularity of XML and Web Services have led to a new generation of document, called Active XML documents (AXML), where some of the information is given explicitly while some of it is given intensionally, by embedded calls to Web Services. Consider as an example an AXML document that represents a Jazz portal. This document contains some extensional data such as a list of Jazz CD’s reviewed by the portal and some intensional data that is not given explicitly but could be materialized by invoking some Web Services, e.g., Jazz CD’s that are reviewed by other portals. The goal of the paper that is summarized here is to provide a formal foundation for AXML documents and to examine fundamental issues they raise.