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ChaPter 2 • underStanding and modeling organizational SyStemS 37

The second area of the use case includes the steps performed and the information required
for each of the steps. These statements represent the standard flow of events and the steps taken
for the successful completion of the use case. It is desirable to write up a use case for the main
path and then to write up one for each of the alternative paths separately rather than using IF …
THEN … statements. Steps are numbered with an integer. The steps may come from a detailed
interview with users or may be derived from agile modeling stories (as described in Chapter 6).
These steps should be reviewed with the users for clarification.
The analyst should examine each of the steps and determine the information required for
each step. If the analyst cannot determine the information, he or she should schedule a follow-up
interview with the user. Some use case descriptions include extensions or alternative scenarios,
with the exceptions as additional sections following the standard flow of events. These are num-
bered with an integer, decimal point, and another integer, such as 3.1, 3.2, 3.3, and so on. These
are steps that may or may not be used. Analysts and users can brainstorm what can go wrong
with the main path, and may uncover important details and conditions. It is necessary to work
with the users to determine what to do when these conditions occur. This helps to detect errors
earlier in the life cycle.
Figure 2.17 illustrates how logic and alternative scenarios can be included in the middle sec-
tion of a use case. In this airline example, notice that step 1 is made up of smaller steps, many
of which are preceded by an “if.” These are still on the main path but occur only if the condition
is met. For example, if there are many airports that serve a city, then all the airports will be dis-
played. Extensions or alternate scenarios can also appear here. For this airline, other scenarios

Figure 2.17
Use cases can include conditional
Steps Performed (Main Path)
1. Information for Steps steps as well as extensions or
Enter departing and arriving airports, dates of travel.
1.1. If an airport code is entered, display matching name, city, country Airport Locations alternative scenarios.
1.2.
If a city is entered, find all matching cities

1.3. Customer selects a city
1.4. If there is more than one airport for the city, display airports
1.5. Client selects an airport
1.6.
Insert the airport code (3 characters)
1.7. Display the matching airport country, city, and airport name
2.
Find all matching flights with available seats
3. Customer selects flight Flight Information
4. Customer logs on
5. Customer Logon
Customer selects passenger names
6. Passenger Records
Seating chart is displayed showing all available seats
7. Plane Number, Seating Chart, Available Seats
Customer selects seat(s) for each passenger
8.
Display confirmation and credit card page
9. Credit card verified
10. Email confirmation sent
11. Airline reservation made
Extensions or Alternative Scenarios
Flight Selection
1. A list of flights displays
2. Customer selects a flight
3. Request is sent to airline
4. Flight is already full
Seat Selection
1. A list of flights displays
2. Customer selects a flight
3. Request is sent to airline
4. Seat reservations are retrieved
5. Seating chart is displayed
6.
Customer cannot find an acceptable seat
Meal Selection for International Flights
1.
Customer selects meal from drop-down list
2. Available Airline Meal List
Record is updated with meal selection
Customer Meal Record