<extend> dependency in UML

Question

Except in the UML context, if A extends B, then B is a subset of A.

But in UML this is the other way around, say, if A extends B, then A is a subset of B,

why is it so strange?

Answer 1

Dependency is <<extend>>used only for use cases. This means that in some cases, one use case extends to another. In the following:

. " " " ". , " " " ".

/.

---

<<extend>> . , !

- , . , :

• .

:
1a. " "
  
1. " "
  

" " case "View Account details" . , -, .

UML, "UML Distilled" . , , , <<extend>>.

Answer 2

( , , - , ), .

- , , . , , , , ( ).

: http://www.agilemodeling.com/essays/useCaseReuse.htm. , . , .

Answer 3

UML "/". "/"; "/".

If B is a generalization of A (that is, A is inherited from B), then A is a subset of B. This should become clear from the is-a relationship: if every A is B, then A is clearly a subset of B. In your terminology, if A extends B, A is a subset of B.

A type is a predicate: for each object you can determine whether it belongs to a predicate. Extending the predicate to make it more restrictive.