Abstract: Data extraction, transformation and loading arc crucial steps of data warehousing, which influences data qualily of data warehouse intensively. With the development of informationization, ETL has already become one of most popular research fields,but till now,ETL theory and technology are still not mature. As to the problems and factors appeared in ETL research, many research methods and achievements were listed according to the main problems existed in each ETL phase. Finally, several future research trends of ETL and some proposals for the future research work were summarized and presented respectively.

Key words: ETL, Data warehouse, Data quality, Metadata