This is an oustanding, clear and comprehensive article which presents several mapping schemes for storing XML documents in relational databases. A total of eight different schemes are presented in detail and other alternative mapping solutions are shortly introduced. Besides, five of these mappings are tested on all the important criteria (size, bulkloading time, running time of queries and updates...) so the results presented help to select the more convenient mapping scheme.
The only points of criticism could be on the models selected for the tests (why testing the Universal schema which is obviously inefficient and not some of the alternative mappings that seem more promising ?) and on the choice of the indices (no results to explain and support these choices).
The result presented here are promising and one can hope that the same research will be done for special purpose XML databases and object-oriented systems in order to determine which type of systems would be the best to store and manage XML data.