An understanding of the following concepts is necessary for querying with Remote Catalogs:

• Catalog: A catalog is a metadata layer that organizes and describes data assets such as schemas and tables. It acts as a bridge between the database and external data sources. A catalog contains one or more schemas, and each schema can have multiple tables. These schemas and tables represent the logical organization of data.

• External Catalogs: they are catalogs that stores metadata for systems other than the locally connected ADB, including other ADBs, remote databases, shares, external data catalogs.

• DB Links: DB Links are a mechanism to connect to a remote database from an Oracle database. They allow you to access tables, views, and other objects in a remote database as if they were local objects. They enable querying data in remote databases. This feature aims to treat DB Links as a type of "catalog." The data dictionary of a remote database connected via a DB Link can be considered a catalog.

• Mounting a Catalog: A mounted catalog is one where the Autonomous Database has an active connection to the catalog, allowing the database to access and query its datasets. Oracle Autonomous Database supports mounting catalogs from external data sources like AWS Glue or Databricks.