Re: Status of UML 2.0, unambigious

Date view Thread view Subject view Author view Attachment view

From: Prof. Dr. Peter H. Schmitt (
Date: Fri 25 Oct 2002 - 09:51:30 BST

Hi Robert,

Here is my contribution to the discussion on UMl being unambiguous.

 From what you wrote I get the impression that you are not using
"unambiguous" in a colloquial sense, but rather in a well defined 
technical sense.

I looked in the book "Introduction to automata theory, languages and
computation" by Hopcroft and Ullman and found on page 87 of the 1979 
edition the definitions you probably had in mind:

   A GRAMMAR G is unambiguous, if for every word w derivable in G, there
   is only one parse tree (i.e. there is essentailly one way to derive w)

   A LANGUGAE L is (inherently) ambiguous if every grammar for L is

Since the semantics of a word w does not depend on the way it is derived
in the grammar, it is perfectly possible that an inherently ambiguous 
language has a well defined formal semantics.

I hope this help to clarify the situation



Bauer, Robert wrote:
> Heinrich,
> But my point is that your goal,
> My understanding of "unambiguous" UML is that each UML diagram has well 
> defined meaning as opposed
> to several meanings depending on who is looking at the diagram. This 
> does (and should not) exclude
> the possibility that the same meaning can be expressed by different 
> diagrams.
> is quite difficult, if not impossible to achieve.
> For example, given some program P, I wish to determine it's meaning.  To 
> do so requires that I have
> a formal semantics, one that is unambiguous and complete in the sense 
> that every sentence constructed
> in the implementation language has only one interpretation in the 
> specification language - but that requires
> me to show that the specification language itself is unambiguous - which 
> in general can't be done.

Prof. Dr. Peter H. Schmitt
Institut fuer LKD                 Fakultaet fuer Informatik
Universitaet Karlsruhe            D-76128 Karlsruhe 

Tel. 0721-608-4000 (Sekr.) -3919  Fax. 0721-608-4211

Date view Thread view Subject view Author view Attachment view