Integrity Checking and Maintenance with Active Rules in XML Databases

While specification languages for integrity constraints for XML data have been considered in the literature, actual technologies and methodologies for checking and maintaining integrity are still in their infancy. Triggers, or active rules, which are widely used in previous technologies for the purpose are still rather untested in XML databases. We present the first steps towards a methodology for design and verification of triggers that maintain integrity in XML databases. Starting from a specification of the integrity constraints plus a collection of XPath expressions describing the possible updates, the method indicates trigger conditions and correctness criteria to be met by the trigger code supplied by a developer or possibly automatic methods. We show examples developed in the Sedna XML database system which provides a running implementation of XML triggers.