Cash represents the money that an agent has in cash. Account represents the accounts of an agent, with an additional slot account.administrator. Account and Credit. Account are two subclasses of account. Account describes the bank account of an agent.
Account describes the credit card account of an agent.
It has one additional slot, limit, that indicates how much credit an agent has. Shop represents the shops in which the buying and selling takes place. The kinds and the number of shops in the system are not limited. Transfer represents the transfers performed in buying and selling. Transfer represents the transfer of items in buying and selling.