The contents of an XML database or an XML/Web data warehouse is seldom static. New documents are created, documents are deleted, and more important: documents are updated. In many cases, we want to be able to search in historical versions, retrieve documents valid at a certain time, query changes to documents, etc. This can be supported by extending the system with temporal database features. In this paper we describe the new query operators needed in order to support an XML query language

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... supports temporal operations. We also describe the algorithms which can make efficient implementation of these query operators possible.