4.7 User-defined types

A user-defined type is a schema object, identified by a <user-defined type name> . The definition of a userdefined type specifies a number of components, including in particular a list of attribute definitions. Although the attribute definitions are said to define the representation of the user-defined type, in fact they implicitly define certain functions (observers and mutators) that are part of the interface of the user-defined type; physical representations of user-defined type values are implementation-dependent.

The representation of a user-defined type is expressed either as a single data type (some predefined data type, called the source type), in which case the user-defined type is said to be a distinct type, or as a list of attribute definitions, in which case it is said to be a structured type.

A user-defined type is described by a user-defined type descriptor. A user-defined type descriptor contains:
 - The name of the user-defined type (<user-defined type name> ). This is the type designator of that type, used in type precedence lists (see Subclause 9.5, "Type precedence list determination").
 - An indication of whether the user-defined type is a structured type or a distinct type.
 - The ordering form for the user-defined type (EQUALS , FULL , or NONE ).
 - The ordering category for the user-defined type (RELATIVE , MAP , or STATE ).
 - A <specific routine designator> identifying the ordering function, depending on the ordering category.
 - If the user-defined type is a direct subtype of another user-defined type, then the name of that user-defined type.
 - If the representation is a predefined data type, then the descriptor of that type; otherwise the attribute descriptor of every originally-defined attribute and every inherited attribute of the user-defined type.
 - An indication of whether the user-defined type is instantiable or not instantiable.
 - An indication of whether the user-defined type is final or not final.
 - The transform descriptor of the user-defined type.
 - If the user-defined type is a structured type, then:
 - Whether the referencing type of the structured type has a user-defined representation, a derived representation, or a system-defined representation.
 - If user-defined representation is specified, then the type descriptor of the representation type of the referencing type of the structured type; otherwise, if derived representation is specified, then the list of attributes.
NOTE 15 - "user-defined representation", "derived representation", and "system-defined representation" of a reference type are defined in Subclause 4.9, "Reference types".
 - If the <method specification list> is specified, then for each <method specification> contained in <method specification list> , a method specification descriptor that includes:
 - The <method name>.
 - The <specific method name>.
 - The <SQL parameter declaration list> augmented to include the implicit first parameter with parameter name SELF.
 - The <language name>.
 - If the <language name> is not SQL, then the <parameter style>.
 - The <returns data type>.
 - The <result cast from type> , if any.
 - An indication as to whether the <method specification> is an <original method specification> or an <overriding method specification> .
 - If the <method specification> is an <original method specification> , then an indication of whether STATIC or CONSTRUCTOR is specified.
 - An indication whether the method is deterministic.
 - An indication whether the method possibly writes SQL data, possibly reads SQL data, possibly contains SQL, or does not possibly contain SQL.
 - An indication whether the method should not be invoked if any argument is the null value, in which case the value of the method is the null value.
NOTE 16 - The characteristics of an <overriding method specification> other than the <method name> , <SQL parameter declaration list> , and <returns data type> are the same as the characteristics for the corresponding <original method specification> .