Which of the following is not a valid statement?

a$.$ Production databases focus primarily on storing historical data and business metrics used exclusively for tactical or strategic decision making.

b$.$ The data warehouse is a specialized database that stores data in a format optimized for decision support.

c$.$ A database that is designed primarily to support a company's day$-$to$-$day operations is classified as an operational database.

d$.$ Online analytical processing is a set of tools that work together to provide an advanced data analysis environment for retrieving, processing, and modeling data from the data warehouse.