What is the approximate time percentage that the ETL process takes when building the data warehouse?

The ETL (Extract, Transform, Load) process is a critical component of building a data warehouse, often accounting for a significant portion of the total project time. Typically, this process can take around 70% of the overall time required to set up a data warehouse.

The reason for this substantial percentage is that ETL involves several complex and time-consuming tasks. Extracting data from various sources, transforming it to ensure it fits the schema of the data warehouse and meets quality standards, and loading it into the warehouse, requires meticulous planning and execution. Data may come from multiple and varied sources, necessitating extensive transformation processes to harmonize formats and automated quality checks.

Additionally, the iterative nature of the ETL process—where refinements and adjustments often need to be made as more data is collected or business requirements change—can also lead to increased time investments. This complexity and need for thorough checking increase the overall time percentage of the ETL process compared to other phases of data warehouse development, such as data modeling or querying. Therefore, estimating that the ETL process takes approximately 70% of the project time reflects the reality of data warehouse projects in practice.