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 formally define the lineage problem, develop lineage tracing algorithms
for relational views with aggregation, and propose mechanisms for performing
consistent lineage tracing in a multi-source data warehousing environment. 
Our results can form the basis of a tool that allows analysts to browse
warehouse data, select view tuples of interest, then ``drill-through'' to
examine the exact source tuples that produced the view tuples of interest.