Explanation:

Answer: (b).
Capturing a subset of the data contained in various operational systems. 

Database extraction is a process of retrieving data from disparate databases. In most cases, companies extract data to process it further or to transfer it to another repository for storage, such as a data warehouse or a data lake. For example, you may perform some calculations on the data (like aggregating sales information) and store the outcome in your data warehouse. This procedure is called ETL (Extract, Transform, and Load). And, extraction is the first important stage in ETL.