1 Lecture 23 – April 11, 2002 Semester end questions More about Bond agents Models and languages supporting concurrency Petri Nets

2 Final Exam and Project The final exam will be Thursday April 25, 7:00 – 9:00 PM in this class room. The class project is due on Monday April 22 at 9 AM. See Projects.html for a description of the format and contents of project. Projects.html

3 Office Hours during the last weeks I will be out of town Sunday April 14 till Saturday, April 20. I will be available on Tuesday, April 24, 3 – 6 PM Thursday, April 15, 4- 7 PM

4 Final Exam Open book Comprehensive Two hours 4-6 problems

5 Final project presentations Tuessday – April 16: 7:00 – 7:20 David Aihe 7:20 – 7:40 Kiran Anna 7:40 - 8:00 Temitope Alo 8:00 - 8:20 Xin Bai Thursday – April 18 7:00 – 7:20 Wafa Elgarath 7:20 – 7:40 Shan Natarajan 7:40 – 8:00 Sudipta Rashit 8:00 - 8:20 Vivek Singh

6 Final project presentations Friday – April 19 CS 232 (Seminar Room) 9:00 – 9:45 John Anthony 9:45 – 10:30 Brian Hill 10:30 – 11:15 Mathew Lowerey 11:15 – 12:00 Aniruddha Tumalla

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11 Agent transformations Trimming. Splitting. Joining.

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15 Place/Transition nets In 1962 Carl Adam Petri introduced a family of graphs, called Place-Transition, P/T nets to model dynamic behavior of systems. P/T nets, are bipartite populated with tokens, that flow through the graph. A bipartite graph is one with two classes of nodes; arcs always connect a node in one class with one or more nodes in the other class. In the case of P/T nets the two classes of nodes are places and transitions; arcs connect one place with one or more transitions or a transition with one or more places.

16 P/T nets Enabling and firing of a transition Weight of flow relations (arcs). Marked P/T net Preset and postset of a transition/place. Modeling choice and concurrency. Confusion – symmetric and asymmetric Marked graph –concurrency but no choice State graph graph – choice but no concurrency Inhibitor arcs – modeling priority

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18 P/T nets Marking  state Finite/infinite capacity nets Strict/weak firing rules Extended P/T nets – P/T nets with inhibitor arcs. Modeling exclusion.

19 Properties on P/T nets Marking independent properties of P/T nets – structural properties Marking dependent properties of P/T nets.

20 State machines Finite state machines can be modeled by a subclass of L-labeled P/T nets called state machines (SM) with the property that In a SM each transition has exactly one incoming and one outgoing arc or This topological constraint limits the expressiveness of a state machine, no concurrency is possible.

21 Marked graphs In a marked graph each place has only one incoming and one outgoing arc thus marked graphs do no not allow modeling of choice.

22 Confusion; free-choice and extended free-choice P/T nets. When choice and concurrency are mixed, we end up with a situation called confusion. Symmetric confusion means that two or more transitions are concurrent and, in the same time, they are in conflict with another one. In an extended free-choice net if two transition share an input place they must share all places in their presets. In an asymmetric choice net two transitions may share only a subset of their input places.

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24 Marking dependent properties Liveness Boundedness Safety Refersibility

25 Firing sequence Rechability analysis

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