We consider the view data lineage problem in a warehousing environment: 
For a given data item in a materialized warehouse view, we want to identify
the set of source data items that produced the view item. We formalize the
problem, and we present a lineage tracing algorithm for relational views with
aggregation.  Based on our tracing algorithm, we propose a number of schemes
for storing auxiliary views that enable consistent and efficient lineage
tracing in a multi-source data warehouse. We report on a performance study of
the various schemes, identifying which schemes perform best in which settings. 
Based on our results, we have implemented a lineage tracing package in the
WHIPS data warehousing system prototype at Stanford. With this package, users
can select view tuples of interest, then efficiently ``drill through'' to
examine the exact source tuples that produced the view tuples of interest.