This paper focuses on modeling the evolution of data for a data warehouse. Digging into the World Wide Web to find behind-the-browser information and to manage this semi-structured data are challenges, and a data warehouse is a good solution to provide an exclusive business environment for mass data storage and management. We observe that there is great similarity between the data model in a data warehouse and XML data. The paper shows how to build a map between data in XML and a data cube in a data warehouse, and it gives an algebra for an XML-based data cube, in order to cope with the evolving data in a data warehouse.