TIMBER: A native XML database.
H. V. Jagadish, Shurug Al-Khalifa, Adriane Chapman, Laks V. S. Lakshmanan,
Andrew Nierman, Stelios Paparizos, Jignesh M. Patel, Divesh Srivastava,
Nuwee Wiwatwattana, Yuqing Wu and Cong Yu.

This paper describes the overall design and architecture of the
Timber XML database system currently being implemented at the
University of Michigan. The system is based upon a bulk algebra
for manipulating trees, and natively stores XML.  New access
methods have been developed to evaluate queries in the XML
context, and new cost estimation and query optimization techniques
have al-so been developed.  We present performance numbers to
support some of our design decisions.

We believe that the key intellectual contribution of this system 
is a comprehensive set-at-a-time query processing ability in a 
native XML store, with all the standard components of relational 
query processing, including algebraic rewriting and a cost-based 
optimizer.