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each execution of the situation), and (4) a description
of the requirements of the situation. Each of these
four components is required to form a complete pic-
ture of the situation.
2.1 The Comparison Shopper Situation
To aid in the articulation of the four components, con-
sider the comparison shopper situation. In the com-
parison shopper situation, a single purchasing agent
that is looking to purchase a particular item and has
multiple potential suppliers to choose from. The pur-
chasing agent is looking for the lowest price and also
has a maximum price that cannot be exceeded. The
sellers each may or may not have the item in question.
If they do have the item, they also have a minimum
selling price.
The agents in the situation will be described as
a set of agent groups. Each group has a set of one
or more roles that the agents in that group are fulfill-
ing. The roles define the abilities of a general class of
agents and since they may be shared between agent
groups they are described separately. In addition,
each group has a defined quantity. The quantity de-
scribes the possible number of agents in that group.
In the comparison shopper situation, the situation has
two groups: one agent group containing the role of
buyer (to be described below) and a quantity of one
and a second agent group containing the seller role
and a quantity of one to ten.
1
To organize the description of the agents in the
system, each situation has one or more roles which
define the capabilities of various types of agents in
the system. They are kept separate from the quantity
of each agent type to allow the description of situa-
tions in which multiple agents share one role, but have
some other differentiation. To enhance the capability
to describe the roles, the roles can be arranged in a
type hierarchy to indicate inheritance. The roles each
describe the actions agents of that role can perform,
the desires that agents of that role would like to fulfill,
and negotiable values that can be used when fulfill-
ing their desires. In the comparison shopper example,
there are three roles. There is a base type called trans-
actor that represents any agent with money and/or
items. In addition, there are two sub-types that are
named buyer and seller. The buyer is capable of giv-
ing money to another agent. The seller is capable of
giving items to other agents. In Figure 1, the roles
are represented as clouds. Within the roles, the give
item and give money actions are represented as light-
ning bolts. In addition to their capabilities, the buyer
and seller each have desires to receive what the other
1
The seller quantity can vary between 1 and 10 agents.
transactor
buyer seller
Requirements
Enviornment
(Data)
buyer
Agent Group
1
seller
Agent Group
1-10
Figure 1: Comparison Shopper Situation.
can give: the buyer has a desire for a give item action
with the buyer agent as the recipient and the seller has
a desire for the give money action with the seller agent
as the recipient. These desires are represented within
the roles as hearts. In addition, both the buyer and the
seller have a negotiable value price which the seller
would prefer to be higher and the buyer would prefer
to be lower.
The environment of a situation can be represented
as a collection of data. This data is composed of three
kinds of data. It includes information that is constant
over all instances of the situation, information that
may be different for different instances of the situa-
tion but is constant throughout the entire timeline of
one execution of the system, and information that may
change as the system executes. In addition, data may
be global to the entire situation or specific to one or
more roles in the situation. In the comparison shop-
per example, there isn’t any global data, but there is
data specific to each role. For example, each trans-
actor agent has a money and item count variable. In
Figure 1, data is represented by cylinders. Each of the
roles has some data that is part of the environment (or
data) of the entire situation.
The final component of the situation model is the
requirements of the system. These include both the
hard requirements that must be met and the soft re-
quirement that the system designer would like to be
met. In the comparison shopper situation the buyers
and sellers must not exceed their price limits; this is
a hard requirement. Another hard requirement is that
money must be given for each item received. Finally,
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