Suppose we now decide we want to add getter and setter messages to <CatalogEntry> for storing the Dewey number. We could go back and define this as a responsibility of the Catalog Entry Thing and regenerate the protocol, but let's try directly adding the responsibility to the protocol.
To add the new messages, follow these steps:
deweyNumber : <String>This is the formal UML syntax declaring a message specification. It indicates a unary message with no parameters that returns an object of type <String>. This is the getter message for the deweyNumber attribute.
deweyNumber: (number: <String>): <String>This is the UML syntax declaring a unary message taking one parameter of type <String> and returning a <String>.