This feature enables you to mark abstract data types used in programs for processing only, for storage only, or for mixed use.

Instances of non-persistable types cannot persist on disk.

A polymorphic table function (PTF) is a new type of table function whose return type is determined by the arguments passed into the PTF.

A table function is a function that returns a collection of rows and that can be called from the FROM clause of a SQL query block. 

The new polymorphic table function (PTF) provides an efficient and scalable framework to extend the analytical capabilities of the Oracle Database. A query writer is able to call these functions without knowing the details of the implementation of the PTF and the PTF doesn't need to know about the details or how the function is being executed (e.g. in serial or parallel) or whether the input rows are partitioned or ordered.

Therefore, a PTF is useful when SQL developers and database administrators want to provide generic extensions which work for arbitrary input tables or queries.

See Overview of Polymorphic Table Functions for more information.

Aggregates and their necessary adjunct, qualified expressions, improve program clarity and programmer productivity.

Through Oracle Database 12c release 2, it was possible to supply the value of a non-scalar datatype with an expression, for example by using the type constructor for a nested table. Starting with Oracle Database Release 18c, any PL/SQL value can be provided by an expression (for example for a record or for an associative array) like a constructor provides an abstract datatype value. In PL/SQL, we use the terms "qualified expression" and "aggregate" rather than the SQL term "type constructor", but the functionality is the same.

See Qualified Expressions Overview and qualified_expression ::= for more information about the syntax and semantics.