Harnessing rCOS for Tool Support—The CoCoME Experience - Formal Methods and Hybrid Real-Time Systems - page 96

3.1 POST—The Common Modelling Example

The point of sale terminal (POST) was originally used as a running example in
Larman's book [20] to demonstrate the concepts, modeling and design of object-
oriented systems. An extended version is now being used as the case study in
the Common Component Modeling Contest (CoCoME) [8].
POST is a computerized system typically used in a retail store. It records
sales, handles both cash payments and creditcardpaymentsaswellasinventory
update. Furthermore, the system deals with ordering goods and generates various
reports for management purposes. The system can be a small system, containing
only one terminal for checking out customers and one terminal for management,
or a large system that has a number of terminals for checking out in parallel, or
even a network of these large systems to support an enterprise of a chain of retail
stores. The whole system includes hardware components such as computers and
bar code scanners, card readers, and a software to run the system. To handle
credit card payments, orders and delivery of products, we assume a Bank and a
Supplier that a terminal can interact with.
The common modelling exercise requires each team to work on a common
informal description of the system, and carry out a component-based modelling
and design. Various aspects should be modelled and analysed, including func-
tionalities, interactions, middlewares, and extra-functionalities (also known as
non-functional requirements) such as timing. Also, code should be generated for
the implementation.
The problem description that we received is largely based on usecasedescrip-
tions . There can be many use cases for this system, depending on what business
processes the client of the system want the system to support. One of the main
use cases is processing sales , that is denoted by the use case UC1 : Process sales .
An informal description can be given as follows.
This use case can perform either express checkout process for customers with
only a few items to purchase, or a normal checkout process . The main course of
interactions between the actors and the system is described as follows.

1. The cashier sets the checkout mode to express check out or for normal check
out. The system then sets the displaylight to green or yellow accordingly.
2. This use case starts when a customer comes to the checkout point with their
items to purchase.
3. The cashier indicates the system to handle a new sale.
4. The cashier enters all the items, either by typing or scanning in the bar code ,
if there is more than one of the same item, the cashier can also enter the
quantity . The system records each item and its quantity and calculates the
subtotal.
In express checkout mode, only a purchase of a limited number of items
is allowed.
5. At the end of entering the items, the total of the sale is calculated. The
cashier tells the customer the total and asks her to pay.
6. The customer can pay by cash or a credit card: