Page Comparison

uses internal formats to represent data entities that it can process. All processing agents (for instance, Analysis and Aggregation) work with these internal formats.

...

internal A {
    int a;
    ...
};
internal B : extends ( A ) {
    int b;
    ...
};

Multiple inheritance inheritances is not supported, i e you can only use the extends or extends_class option once in the definition of an internal format. 

...

It is possible to declare user-defined event types in Ultra by using the event keyword instead of internal. Such an event is a special type of internal format with added event processing support.