[Modeling] Re: Comments on interaction diagram modeling doc

[Stephen Cranefield]

Lin Padgham wrote:
> 2.3.1 senders and receivers of messages can have same or different
>     roles. What assumptions do we want to make about same roles being
>     different agents. I would suggest an assumption that if a message is
>     shown going to the same role, then the assumption is that it is to
>     a different agent in that role - or at least that it is not only
>     to itself. I.e. it may be a message sent by one agent in a role X,
>     to all other agents in role X, including itself. However you
>     wouldn't show a message if it was a single agent sending a message
>     to itself.

I find it useful on ordinary UML sequence diagrams to be able to show
messages from an object to itself, in order to indicate local
processing within the thread of control of that object.  It would be a
shame not to have a similar ability in AUML, even though a "message to
self" would probably eventually be implemented using a more efficient
mechanism than inter-agent messaging.

One of the useful features about UML is that it can be used informally
to sketch out ideas, because there aren't too many constraints on how
it is used.  Although I agree that we we will need to define precise
semantics for AUML, I don't think we should be aiming to constrain its
use any more than is necessary for that purpose.

> I think something that addresses the concept captured by break is
> important, but i would prefer some mechanism that indicates an
> exception point and allows the exception behaviour itself to be
> defined separately: Often exception behaviour is the same for many
> places/protocols, it occurs often and clutters up the view of the
> normal execution of the protocol.  It needs to be defined clearly, but
> should be extracted out. Some way to name an exception point (a bit
> like a merge point) and then define it elsewhere would be good.

I agree with this.

- Stephen