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110 GIORGINI, KOLP, AND MYLOPOULOS
Figure 7.8 The Information Broker of Medi@

maker applies the matchmaker pattern to locate the appropriate source for the Information Broker,
and the monitor pattern is used to check any possible change in the Product Database. Finally,
the mediator pattern is applied to dispatch the interactions between the Information Broker, the
Source Matchmaker, and the Wrapper, while the wrapper pattern forms the interaction between
the Information Broker and the Product Database.
Figure 7.8 shows the remote administrative tool for the information broker of Figure 7.7. The
customer sends a service request to the broker requesting the buying or selling of DVDs. He/she
chooses which DVDs to sell or buy, selects the corresponding DVD titles, the quantity and the
deadline (the timeout before which the broker has to realize the requested service). When receiv-
ing the customer’s request, the broker interacts with the media shops. The interactions between
the broker and the media shops are shown in the bottom-right corner of the figure.
To go deeper into the details, the rest of the section concentrates only on the Store Front ac-
tor. Figure 7.9 depicts a partial, extended UML class diagram (Castro, Kolp, and Mylopoulos,
2002) focusing on the actor that will be implemented as an aggregation of several CartForms and
ItemLines.
To specify the checkout operation identified in Figure 7.9, extensions of interaction diagrams
(Castro, Kolp, and Mylopoulos, 2002) allow us to use templates and packages to represent checkout
as an object, as well as in terms of sequence and collaborations diagrams.
Figure 7.10 focuses on the protocol between Customer and Shopping Cart, which consists of a
customization of the FIPA Contract Net Protocol (Odell, Van Dyke Parunak, and Bauer, 2000). Such
a protocol describes a communication pattern among actors as well as constraints on the contents of
the messages they exchange. When a Customer wants to check out, a request-for-proposal message