Data warehousing is a place where data collected from multiple sources is stored. The data in a data warehouse comes from data marts that collect data after interaction with the users, operating systems, and flat files. It consists of raw data, metadata, and summary data. Data from various databases are integrated using a query-driven and update driven approach. It is non-volatile, subject-oriented, and time-variant. The functions of a data warehouse are data extraction, cleaning, transformation, and loading. OLTP and OLAP operations on the data are performed for processing. Data warehouse architecture is of 3 types: single-tier, two-tier, and three-tier.