95-843 Service Oriented Architecture          Homework 1

Due: Midnight Thursday, March 27, 2008

Fundamental Issues
==================

Please review the chapter on Petri nets from the Johnsonbaugh
text (PetriNetIntro.pdf)  and read the article by Hamadi on web 
service composition using Petri nets. Both of these are provided on the 
course schedule.

Submit a Word document or scanned drawings containing your 
answers to the digital drop box on blackboard.

Model the following algorithms with a Petri net. Provide a 
marking that represents the situation prior to execution of
the algorithm.

1. A = 1
   B = 2
   C = A + B
   C = C + 1

2. A = 2
   B = A + A
   C = 3
   D = A + A
   C = A + B + C

3.     A = 1
       S = 0
   10  S = S + A
       A = A + 1
       GOTO 10

4. Wash a lion:

   1. Get lion.
   2. Get soap. (real soap not SOAP)
   3. Get tub.
   4. Put water in tub.
   5. Put lion in tub.
   6. Wash lion with soap.
   7. Rinse lion.
   8. Remove lion from tub.
   9. Dry lion.

5. Show that the marking M of Figure 8.5.10 of Johnsonbaugh is live 
and bounded.

6. Consider Exercises 8 on page 477 and 11 on page 478 of Johnsonbaugh.

   a) Which transitions are enabled?
   b) Show the markings that result from firing t1.
   c) Is M live?
   d) Is M safe?
   e) Is M bounded?
   f) Show or describe all markings reachable from M.
   g) Exhibit a marking (other than the marking that puts zero tokens
      in each place) not reachable from

7. Develop an alternative Petri net model for the situation of Example
   8.5.10 that prevents deadlock.

8. Describe the following web service in words: 
   Ref(S1, assess_claim, [A1:An])

9. Prove statement (20) of the Service Algebra studied in class.

10. Prove statement (21) of the Service Algebra studied in class.