BON

class_chart ACCOUNT
  description: "A simple bank account."
  query
    "What is the balance?", Balance: REAL
    "What is the account holder name?", Holder: STRING
    "Is the account active?", Active: BOOLEAN
  command
    "Deposit the given amount.", Deposit (amount: REAL)
    "Withdraw the given amount.", Withdraw (amount: REAL)
    "Close the account.", Close
  constraint
    "Balance is non-negative", Balance >= 0.0
end

class_chart BANK
  description: "A financial institution managing accounts."
  query
    "How many accounts does the bank have?", Account_count: INTEGER
    "Does the bank hold a given account?", Has_account (id: INTEGER): BOOLEAN
  command
    "Open a new account for the given holder.", Open_account (holder: STRING)
    "Close a specific account.", Close_account (id: INTEGER)
  constraint
    "Account count is non-negative", Account_count >= 0
end