Extending XML Types Using Updates

Abstract

The XML Messaging Protocol, a part of the Web service protocol stack, is responsible for encoding messages in a common XML format (or type), so that they can be understood at either end of a network connection. The evolution of an XML type may be required in order to reflect new communication needs, materialized by slightly different XML messages. For instance, due to a service evolution, it might be interesting to extend a type in order to allow the reception of more information, when it is available, instead of always disregarding it. The authors’ proposal consists in a conservative XML schema evolution. The framework is as follows: administrators enter updates performed on a valid XML document in order to specify new documents expected to be valid, and the system computes new types accepting both such documents and previously valid ones. Changing the type is mainly changing regular expressions that define element content models. They present the algorithm that implements this approach, its properties and experimental results.