Calcite is a highly customizable engine for parsing and planning queries on data in a wide variety of formats. It allows database-like access, and in particular a SQL interface and advanced query optimization, for datanot residing in a traditional database.
Apache Calcite is a dynamic data management framework.
It contains many of the pieces that comprise a typical database management system, but omits some key functions: storage of data, algorithms to process data, and a repository for storing metadata.
Calcite intentionally stays out of the business of storing and processing data. As we shall see, this makes it an excellent choice for mediating between applications and one or more data storage locations and data processing engines. It is also a perfect foundation for building a database: just add data. Source