Metadata management is an essential factor in data warehousing. In data warehousing environments, data is transformed and integrated into a single database from multiple autonomous and heterogeneous data sources. What kind of metadata can be used for expressing the multiplicity of data models and the data transformation and integration processes in such environments? How can this metadata be further used for supporting other data warehouse activities? We examine how these questions are addressed by AutoMed, a system for expressing data transformation and integration processes in heterogeneous database environments.