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ChaPter 2 • underStanding and modeling organizational SyStemS 25

Figure 2.4
The basic symbols of a data flow
diagram.
A process means that some action
or group of actions take place.

An entity is a person, group,
department, or any system that
either receives or originates
information or data.

A data flow shows that information
is being passed from or to a
process.

In Chapter 7 we see that a data flow contains much information. For example, the passenger
reservation contains the passenger’s name, airline, flight number(s), date(s) of travel, price, seat-
ing preference, and so on. For now, however, we are concerned mainly with how a context level
data flow diagram defines the boundaries of the system. In the preceding example, only reserva-
tions are part of the process. Other decisions that the airline would make (for example, purchas-
ing airplanes, changing schedules, pricing) are not part of this system.
The context-level data flow diagram is one way to show the scope of the system, or what
is to be included in the system. The external entities are outside the scope and something over
which the system has no control.

Systems and the Entity-Relationship Model
Another way a systems analyst can show the scope of a system and define proper system bound-
aries is to use an entity-relationship model. The elements that make up an organizational system
can be referred to as entities. An entity may be a person, a place, or a thing, such as a passenger
on an airline, a destination, or a plane. Alternatively, an entity may be an event, such as the end

Figure 2.5
Preferences and
Available Flights Travel A context-level data flow diagram
Passenger Agent for an airline reservation system.

0
Travel Request Ticketing Information
Airline
Reservation
System

Passenger
Reservation

Airline