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					    Aspect-Oriented Software Development (AOSD) - 236608

                                    Homework 2
                                   (Due on 18/03/08)



The goal of this assignment is to give you an experience in:
       - detecting “natural” and useful aspects for a given system
       - writing different kinds of aspects in AspectJ
       - describing aspects by assume-guarantee specifications
       - determining aspects categories

Submission guidelines:
   1. The submission is in pairs, both electronically and by a hard copy.
   2. The submission should include:
         a. code of the aspects
         b. documentation (short comments inside the code)
         c. sample execution output
         d. (only in the hard-copy, of course) – answer to Question 2.


Question 1:

Task description:
You are given a base system, which is far from being perfect and can be improved, in
a natural way, by adding aspects to it. Your task is to write at least four aspects for
this system, while the following criteria should be met:
  - Among the (at least) 4 aspects you write there should be at least one aspect of each
category (spectative, regulative, weakly invasive and strongly invasive)
  - There should be at least one case of "aspect applied over another aspect", that is, a
join-point of some aspect should occur in the advice of another aspect.
  - There should be at least one potentially reusable aspect: aspect that can be
reasonably reused for some other base system, for example – for the RationalExam
system from Home task 1.
  - The aspects should be natural. In other words, adding this particular aspect to this
particular system should make sense and even be useful.
  - The aspects should not be trivial (extra points will be added for originality and non-
triviality of the aspects).
You are allowed, but do not have to add functionality to the base system in order to
enable (and justify) adding your aspects.

Base system description:
The system given is a shopping mall parking system. The parking of the shopping
mall has three entrances, and three exits. At each entrance there is a ticket automat
that prints entrance tickets for the drivers. The ticket stores the arrival time. At each
exit there is a payment machine, which collects the ticket from the driver, calculates
the payment and opens the gate after the payment is received (only exact payment is
accepted).
Question 2:

For each of the aspects you write, answer the following questions:

   a. What is the category of the aspect? Explain.
   b. Is it potentially reusable?
   c. Write a possible assume-guarantee specification of the aspect (informally -
      just a couple of sentences in natural language)



Good luck!

				
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