To show the sequence of events involved in adding a book to the catalog, you must now add figures representing the method calls between the objects in the diagram. Each figure shows a single method call between a sender and a receiver, as well as the return after the method has completed. In addition, the sequence diagram also shows activation on each object's lifeline, so you can see which objects are active (that is, which objects are currently executing in response to method calls) at any given time.
In general terms, the sequence of events involved in adding a book to the catalog goes something like this: