A data warehouse is a centralized repository for aggregating data of different types for further analysis. Data from different source databases are loaded into a data warehouse by a process called Extract Transform Load (ETL). Extracting is the process of pulling some or all of the data out of the source databases. Transforming includes various aspects of processing, including data cleaning and structuring the data to adhere to a common format. Loading the data is the process of moving the data into the warehouse.