|Description||string||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.
- 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.
- 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.