A structured type is a user-defined data type that has a structure that is defined in the database. It contains a sequence of named attributes, each of which has a data type. A structured type may be defined as a subtype of another structured type, called its supertype. A subtype inherits all the attributes of its supertype and may have additional attributes defined. The set of structured types that are related to a common supertype is called a type hierarchy and the type that does not have any supertype is called the root type of the type hierarchy.
A structured type may be used as the type of a table or a view. The names and data types of the attributes of the structured type become the names and data types of the columns of this typed table or typed view. Rows of the typed table or typed view can be thought of as a representation of instances of the structured type.
A structured type cannot be used as the data type of a column of a table or a view. There is also no support for retrieving a structured type into a host variable in an application program.