Creating Object Types: Syntax

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Object Type
It is an Oracle database construct, managed via DDL extensions, that defines a data structure (attributes) and the legal operations (methods) on the attributes. The type is only a template and holds no data itself; you may create variables, tables, columns, and other constructs of this type.


Attribute
It is a structural part of an object, roughly akin to a column in a table.

• Each attribute must be of a single datatype, either scalar, like VARCHAR2 or INTEGER, or composite, like a user-defined nested table.
• User-defined types must have one or more attributes.
• Attributes are named and have a datatype.
• Attribute names must be unique within a user-defined datatype definition.
• Attribute datatypes can be an object type or a built-in datatype.

Method
It is a procedure or function that operates on an object’s attributes.

• The methods for an object can only be invoked in the context of a specific object of that type.
• There is a special default method supplied by Oracle, a constructor, that initializes objects.
• Method implementation may be coded in PL/SQL or in a 3 GL such as Java and C/C++ and being invoked as an Oracle “external procedure.”
• Methods are similar to Oracle functions, procedures, and packages.