1. Abiteboul, S., Hull, R., Vianu, V.: Foundations of Databases. Addison-Wesley, Reading (1995)
2. Möller, A., Schwartzbach, M.: An Introduction to XML and Web Technologies. Addison Wesley, Reading (2006)
3. Beyer, K.S., Cochrane, R., Josifovski, V., Kleewein, J., Lapis, G., Lohman, G.M., Lyle, R., Özcan, F., Pirahesh, H., Seemann, N., Truong, T.C., der Linden, B.V., Vickery, B., Zhang, C.: System RX: One Part Relational, One Part XML. In: SIGMOD, pp. 347–358. ACM, New York (2005)
4. Fan, W.: XML Constraints: Specification, Analysis, and Applications. In: DEXA Workshops, pp. 805–809. IEEE Computer Society Press, Los Alamitos (2005)
5. Buneman, P., Davidson, S.B., Fan, W., Hara, C.S., Tan, W.C.: Reasoning about keys for XML. Information Systems 28(8), 1037–1063 (2003)