Synchronizing XPath views

The increasing availability of XML-based data sources, e.g., for publishing data on the WWW, means that more and more applications (data consumers) rely on accessing and using XML data. Typically, the access is achieved by defining views over the XML data, and accessing data through these views. However, the XML data sources are often independent of the data consumers and may change their schemas without notification, invalidating the XML views defined by the data consumers. This requires the view definitions to be updated to reflect the new structure of the data sources, a process termed view synchronization. XPath is the most commonly used language for retrieving parts of XML documents, and is thus an important cornerstone for XML view definitions. This work presents techniques for discovering schema changes in XML data sources and synchronizing XPath-based views to reflect these schema changes. In many cases, this allows the XML data consumers to continue their operation without interruption. Experiments show that the techniques work well even if both schema and data change at the same time. To our knowledge, this is the first presented technique for synchronizing views over XML data.