Figure 7.11 An activity diagram representing the use case Book a flight. (continues)

7.5 The Use Case Specification Document 143

Enter URL

System displayshome page

Enter flight datasearch flights

System displaysairport page

Select airports

Change searchcriteria

System displaysoutbound flights

Include nearbyairports?

Do you want to changesort criteria?

No

No

Yes

Yes

Select a flight

Confirm the flight

System displaysreturn flights

Save itinerary

System displaysdetail of the flight

Do you want to saveitinerary and exit?

No

Yes

Yes Do you want to change return flight?

No

Do you want to changeoutbound flight?

No

Select returnflight

Yes

Figure 7.11 An activity diagram representing the use case Book a flight. (continued)

State Machine DiagramsSometimes we may need to describe the behavior of objects that act differently depending ontheir state. In this case we can use UML 2 state machine diagrams [AMB04]. In previous ver-sions of UML, these diagrams were called state chart diagrams, and in other modeling languages,they are called state-transition diagrams or just state diagrams.

UML state machine diagrams depict the various states that an object may be in and the tran-sitions between those states. For example, an object Flight may be in the state Reserved orBooked.

The rounded rectangles represent states. The arrows represent transitions from one state toanother triggered by an event. Dark circles represent initial and final states.

This section of the use case document is optional.

144 Chapter 7 Creating Use Cases

Confirm the flight

Log in

System displaysavailable seats

Provide passengerinformation

Register

Enter billinginformation

System providesconfirmation number

Are you a newuser?

No

No

Yes

Yes

Is ID available?

No

Yes

Is passwordcorrect?

Select seats