UML Designer User's Guide
The first method call on a sequence diagram must originate from the
system activation at the left edge (only an active object can send a message
to another object). This initial method call represents a call from
outside the diagram; in our diagram, it represents input from an outside
actor initiating the cataloging operation. We have not yet defined an
actual method for Library that would accept external input, so for
now we can use the standard yourself method as a
placeholder. This method call does not itself have any
significance; it is used simply to activate the Library
object.
To add this method call to the diagram, follow these steps:
- Select
Method call from the tool bar.
- Click mouse button 1 on the system activation to indicate the source of
the message (in this case, an object outside the diagram).
- Click mouse button 1 on the Library object's lifeline to
indicate the receiver of the message.
- When prompted to choose a method, select Object in the
Classes list, Object in the Protocols list,
and #yourself from the Messages list. This
indicates that the yourself method (inherited from
Object and defined in the <Object> protocol) is the
target of the call.
- Select OK. The method call to yourself, and
its return, appear as a method call figure. In addition, the
Library object's lifeline now shows activation between the
message send and return.

- Select the activation for the yourself method call on the
Library object's lifeline.
- Use mouse button 1 to drag the bottom selection handle downward,
lengthening the activation. (The activation of the Library
object lasts for the duration of the cataloging operation.)
As you add more method calls, you can continue to lengthen the activation
as needed. You can also move a method call and its associated
activation up or down by dragging the center of the activation.
[ Top of Page | Previous Page | Next Page | Table of Contents | Index ]