Final answer:
In Oracle 12c, a database schema is a collection of database objects that are associated with a database user. It organizes and secures the database by controlling access and is essential for efficient database management and performance.
Step-by-step explanation:
A database schema is a defined, self-contained structure in Oracle 12c.
In Oracle 12c, a schema is a collection of database objects, which can include tables, views, sequences, synonyms, indexes, clusters, database triggers, procedures, functions, packages, materialized views, and database links. A schema is associated with a database user and has the same name as that user. Each user has a single schema. The schema helps in organizing and securing the database by allowing administrators to control user access to database objects.
The structure of a schema in Oracle 12c is critical as it defines how the data is stored, accessed and managed within the database environment. Proper schema design can greatly improve database performance and facilitate more efficient data retrieval.