Colorful XML. Divesh Srivastava. XML has a tree-structured data model and permits a wide variety of schema design alternatives. At one extreme, normalized shallow schemas help eliminate update anomalies but do not permit effective use of XPath's rich twig patterns. At the other extreme, redundant deep schemas support concise XPath query expression, but are prone to update anomalies. Can one have the best of both worlds? We show that this is indeed possible using the multi-colored trees (MCT) data model, which is a natural extension of the XML data model. In MCT, data is modeled as a superposition of multiple trees, each with its own color. We develop algorithms for transforming ER diagrams into MCT schemas that simultaneously satisfy the schema design goals of anomaly avoidance and concise query expression. XQuery can also be easily extended to navigate and restructure the superposition of colored trees. MCT has been implemented on top of Timber, the native XML database from the University of Michigan. Experimental evaluation using this prototype implementation and a wide variety of ER diagrams validates the benefits of the MCT design methodology. Not only are MCT queries and updates more succinct and easier to express than on an equivalent shallow XML schema, but they can also be much more efficient to evaluate than on equivalent deep and shallow XML schemas. This is joint work with H. V. Jagadish, Laks V. S. Lakshmanan, Monica Scannapieco and Nuwee Wiwatwattana.