The short answer to this query; it depends on what type of data you use within your respective business. For most modern use cases, data is being collected and stored in a source system or software. Accessing the data from the source system can often be done programmatically through an API, manual CSV, Excel, JSON, or flat file exports, or, if the developers of the source wanted to make it easy, direct connection to a database. To get that data into a data warehouse, two of the most common data warehouse strategies currently on the market; the ETL and the ELT methods.