> -----Original Message----- > From: Eric D. Tarkington [mailto:[EMAIL PROTECTED]] > Sent: 15 April 2002 22:40 > To: ROSE_FORUM > Subject: (ROSE) Bar Bet #4 > > > > ...or anyway, I think it's 4. It's been such a long time > since my last > one. > > As usual, the bar bet is on a controversial question that should be > obvious to everyone, dammit, but the instructors at Seneca College > disagree with each other. I will try to state opposing positions > even-handedly, and will only confess my "side" only after others have > stated some opinions. > > Here's the bet: In sequence diagrams, you should not send messages to > actors. > > THIS IS OBVIOUSLY TRUE! When you send a message in a > sequence diagram, > you are saying that the receiving object has an operation. This is > probably the main payoff of sequence diagrams: they reveal the > operations and how to coordinate them. Actors are either > human or just > external, and we can't build operations into them either way. > This is a > basic difference between actors and objects.
The basic difference between actors and objects is not in what ~they~ can and can't do. The difference is in what ~you~ can and can't do with them. The classes describe the system being designed. You have full control over what they will do or won't do. Their interfaces are fluid as far as your system design is concerned. The actors are outside your system. You have no control over them whatsoever. Their interfaces are fixed outside your current model. Hence, the process of changing their interfaces is outside the scope of this model. Your model has to cope with those interfaces. So, both actors and classes have interfaces. Actors' interfaces are more limited in scope, granted (you don;t go around instantiating them, for instance), but they can still receive and send messages. > > THIS IS OBVIOUSLY [CENSORED TO AVOID UPSETTING OUR FIREWALL -- hfa]! When you send a message to an actor, you are > showing necessary timing relationships between messages, which is a > crucial feature of correct sequence diagrams. End of discussion. How else would you describe a system's communication with the outside world? The actors' interfaces dictate the protocol for talking to them. The messages between your system and the actors describe how you use that protocol. Even human actors have an interface (the UI) and they exchange messages with the system: They ~enter~ data and the system ~displays~ information to them, at its most basic. > > OK, folks, what do you think? There is a virtual beer in it for a > correct answer, but you have to make a clear winning argument! Mine's a Newky Ex. It's virtually unavailable outside of North East England, anyway, so a virtual pint won't set me back any further. > -Eric Best regards, H�seyin Angay Karabash Ltd. www.karabash.co.uk > ************************************************************** > ********** > * Rose Forum is a public venue for ideas and discussions. > * For technical support, visit http://www.rational.com/support > * > * Post or Reply to: [EMAIL PROTECTED] > * Subscription Requests: [EMAIL PROTECTED] > * Archive of messages: > * http://www.rational.com/support/usergroups/rose/rose_forum.jsp > * Other Requests: [EMAIL PROTECTED] > * > * To unsubscribe from the list, please send email > * To: [EMAIL PROTECTED] > * Subject: <BLANK> > * Body: unsubscribe rose_forum > ************************************************************** > *********** > This private and confidential e-mail has been sent to you by Egg. The Egg group of companies includes Egg Banking plc (registered no. 2999842), Egg Financial Products Ltd (registered no. 3319027) and Egg Investments Ltd (registered no. 3403963) which carries out investment business on behalf of Egg and is regulated by the Financial Services Authority. Registered in England and Wales. Registered offices: 1 Waterhouse Square, 138-142 Holborn, London EC1N 2NA. If you are not the intended recipient of this e-mail and have received it in error, please notify the sender by replying with 'received in error' as the subject and then delete it from your mailbox. ************************************************************************ * Rose Forum is a public venue for ideas and discussions. * For technical support, visit http://www.rational.com/support * * Post or Reply to: [EMAIL PROTECTED] * Subscription Requests: [EMAIL PROTECTED] * Archive of messages: * http://www.rational.com/support/usergroups/rose/rose_forum.jsp * Other Requests: [EMAIL PROTECTED] * * To unsubscribe from the list, please send email * To: [EMAIL PROTECTED] * Subject: <BLANK> * Body: unsubscribe rose_forum *************************************************************************
