The Extended Example

1
The Extended Example

• Chapter 5
• Formal Specification using Z

2
Full definition of boarding operation

• The definition of the boarding and disembarking
  operations did not consider what what was to
  happen when the precondition of an operation was
  not fulfilled. To handle this we will include a
  variable reply of type RESPONSE for each
  operation.
• RESPONSE OK twoErrors onBoard full
  notOnBoard
• The reply variable will indicate what is
  happening during an operation.

3
Full definition of boarding operation

• Either
• p is not on board and the aircraft is not full
  and p gets included in onboard and reply is OK.
• OR p is on board and the aircraft is full and
  onboard is unchanged reply is twoErrors.
• OR p is on board and the aircraft is not full
  and onboard is unchanged reply is onBoard.
• OR p is not on board and the aircraft is full and
  onboard is unchanged reply is full.

4
Full definition of boarding operation

• p PERSON, reply RESPONSE
• (p onboard L onboard lt capacity L
• onboard onboard U p L reply OK)
• v
• (p onboard L onboard capacity L
• onboard onboard L reply twoErrors)
• v
• (p onboard L onboard lt capacity L
• onboard onboard L reply onBoard)
• v
• (p onboard L onboard capacity L
• onboard onboard L reply full)

5
Full definition of disembark operation

Either p is on board and p gets removed from
onboard and reply is OK. OR p is not on board
and onboard is unchanged reply is
notOnBoard. p PERSON, reply RESPONSE (p
onboard L onboard onboard \ p L reply
OK) v (p onboard L onboard onboard L
reply notOnBoard)
6
Recall from chapter 2

• Certain people are registered as users of a
  computer system. At any given time, some of these
  users are logged in to the computer. There is a
  limit (unspecified) to the number of users logged
  in at any one time. All users are either staff
  users or customers.

7
Chapter 5 Exercise 1Practice

• Referring to question 1 chapter 1, and its
  development in the exercises of chapter 3 (given
  on the previous slide), give full descriptions,
  including possible unfulfilled preconditions, in
  the manner of this chapter.
• 1. A suitable type for the response from any of
  the following operations.
• 2. The operation to register a new user.
• 3. The operation to remove a user.
• 4. The operation to log in.
• 5. The operation to log out.

8
Chapter 5 Solution Exercise 1

• 1. A suitable type for the response from any of
  the following operations.
• RESPONSE OK AlreadyAUser NotAUser
  LoggedIn notLoggedIn

9
Chapter 5 Solution Exercise 2

• 2. The operation to register a new user.
• reply RESPONSE, pPERSON
• loggedIn loggedIn
• L
• ((p users L
• users users U p L
• reply OK)
• v
• (p users L
• users users
• reply AlreadyAUser)