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CounterFrame counter # new CounterFrame(proxy);;
BarCodeReaderUI reader # new BarCodeReaderUI();
The test consists of a sequence of steps similar to those performed in the
previous prototype. In addition the acquisition of all the products (with
codes 1 through 3) should be simulated. To pass the test we need to check
the coherence between the types of products, the quantity and the total of
the check.
Prototype 3: Distributed system
This prototype addresses a new concern: the distribution of the system.
There are several counter terminal devices that are separated from the
central server. A simple protocol is designed to support the interactions
between each terminal and the server.
The functional requirement for the communication protocol between the
counter terminals and the central server is to support the basic operations of
the counter user interface, which are codified by the MarketProxy interface
defined in the previous prototype. In particular the operations are: connect,
product info, set customer, acquire product, end transaction and disconnect.
The main constraint for the communication protocol is to occupy a
limited network band. The size of the messages exchanged by the protocol is
limited by Equation 14.1.
The design of this prototype is divided into two main parts: the design of the
data exchange protocol and the design of the software infrastructure. The
former is developed from scratch while the latter builds on the previous
Decision point
What protocol do we use?
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