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CSC 236            Homework Exercise 6 -- Marking Scheme        Winter 2008
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NOTE TO STUDENTS:

You will find below the marking scheme used for your homework, including
the meaning of marking codes and number of marks associated with each one.
This file also contains my instructions to the marker (so you can get an
idea of how the homework was marked) and the marker's comments about each
question.

Please take the time to read this carefully before you ask questions about
the grading of your homework.


NOTE TO MARKER:

Be picky!  On any homework, it is the responsibility of students to show
that they understand how to solve each problem and to write up their
answers carefully.  At the same time, keep in mind that exercises are worth
only 1.5% of the final grade, so your marking should be somewhat coarse.

For each question, I list solution elements with an associated code for
writing on student papers (the letter(s) between underscores _) and a
number of marks.  There are also general errors (with associated codes)
given below, with a maximum number of marks to take off for each type of
general error (as a percentage of the value of the question).  You will
likely encounter other common errors, or maybe decide to break down the
marking scheme further.  Simply make note of these changes/additions to
the marking scheme, and introduce new code letters (or short words) to
allow you to quickly give accurate feedback to the students (both in terms
of what they did wrong and how many marks it cost them).


GENERAL ERRORS (marked negatively, in addition to any other errors):

    _A_rithmetic/_A_lgebra [up to 10%]:  calculation error

    _N_otation [up to 20%]:  incorrect/ambiguous notation

    _V_agueness [up to 20%]:  incorrect/unjustified/vague claim

General marker's comments:

 -  _M1_:  Not enough justification.  When you need to show that a string
        is in L(R), where R is some regular expression, you have to
        explicitly explain how to construct the string.

 -  _M2_:  Not enough justification.  When you need to show that a string
        is not in L(R), where R is some regular expression, you have to
        prove it.  A proof is a convincing demonstration of a well
        structured argument.  Please read examples from your notes.

 -  _M3_:  Not enough justification.  Correctness of a RE has to be proved,
        or at least reasonably explained.

 -  _M4_:  Not enough justification.  You had to explicitly write what is
        the meaning of each state in your FSA.


1.  [6 marks]

    For each part:

    _A_nswer [.5 marks]:  correct answer.

    _J_ustification [1 mark]:  reasonable explanation.


2.  (a) [3 marks]

    _FSA_ [2 marks]:  correct FSA with reasonable justification (clear
        meaning for each state).

    _RE_ [1 mark]:  correct RE with reasonable justification (give marks
        for missing justification if correctness is really obvious).

    (b) [6 marks]

    _FSA_ [2 marks]:  correct FSA with reasonable justification (clear
        meaning for each state).

    _RE_ [4 marks]:  correct RE [2 marks] with reasonable justification
        [2 marks].