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IT533 - SOFTWARE ARCHITECTURES - CLASS 3
SYSTEM INTERFACE CHOICES AND PRACTICAL EVENTS

To: (Stimulus) (Response)

Stimulus (Top)

When the system architecture is determined, the decision may be made to accept the stimulus for an essential event on multiple media types with multiple delivery mechanisms. Because the method used to detect a stimulus will be different for each media type and delivery mode, a separate practical event will be required for each combination of interface technology.

For example, consider the essential event:

Event: Customer Places Order
   Message Stimulus:   Receive Order from Customer.
   Update Response:   Enter order into system state.
   Message Response:   Send order to shipping department.

Now, suppose that when we develop the interface model, we decide on the following technology choices for the order stimulus:

Connection
Type
Media
Type
Delivery
Type
Manual Paper Order Form United States Mail
Express Service
Fax
Manual Voice Telephone
Automated Web Page Order Form Internet

Since there are three media types, the essential event will need to be mapped into at least three practical events. And, since each of the paper delivery types will require a different detection method, each mode may lead to a separate practical event. Thus, the partially practical event list would be:

Event: Customer Places Order by Mail
   Message Stimulus:   Receive Mail Order from Customer
   Update Response:   Enter order into system with entered state.
   Message Response:   Send order to shipping department.

Event: Customer Places Order by Fax
   Message Stimulus:   Receive Fax Order from Customer
   Update Response:   Enter order into system with entered state.
   Message Response:   Send order to shipping department.

Event: Customer Places Order by Express
   Message Stimulus:   Receive Express Order from Customer
   Update Response:   Enter order into system with entered state.
   Message Response:   Send order to shipping department.

Event: Customer Places Order by Phone
   Message Stimulus:   Receive Phone Order from Customer
   Update Response:   Enter order into system with entered state.
   Message Response:   Send order to shipping department.

Event: Customer Places Order by Internet
   Message Stimulus:   Receive Internet Order from Customer
   Update Response:   Enter order into system with entered state.
   Message Response:   Send order to shipping department.

At this stage in the process, each event has the same responses. But, this may change as additional layers of design choices are made.

Responses (Top)

Note that it is not necessary to have a separate event when the response must be delivered using different modes and media types. Remember that an event can have only one stimulus but it can have multiple responses and we can place conditions on which responses are generated.

For example, consider the following essential event:

Event: Shipping Ships Order
   Message Stimulus:   Receive Shipped Notice from Shipping.
   Update Response:   Update order state to shipped.

Now, suppose that we decide to notify our internet customers when their order is shipped so that they can plan for its arrival. Then, the practical event is:

Event: Shipping Ships Order
   Message Stimulus:   Receive Shipped Notice from Shipping.
   Update Response:   Update order state to shipped.
   Message Response:   Send Shipped Notice Email to Customer [if order arrived by Email]


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Prepared by David L. March -- Last Revised on April 13, 2003
COPYRIGHT © 1999-2003 BY DAVID L. MARCH