16-17 May 2019 • Sofia, Bulgaria

Submission: 21 February 2019Notification: 11 March 2019Final Version: 1 April 2019

Transition

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A GN transition with m inputs and n outputs

Transition in the context of generalized nets is an object from the static structure of the net, which comprises the conditions of tokens' transfer from the transition's input places to its output places.

When tokens enter the input place of a transition, it becomes potentially fireable and at the moment of their transfer towards the transition's output places, the transition is being fired.

The tokens' transfer through a transition is described by a special formal algorithm.

Formal description

Formally, every transition is described by a 7-tuple:

Z = \langle L', L'', t_1, t_2, r, M, \Box \rangle

where:

  • L', L'' are finite, non-empty sets of places: the transition's input and output places, respectively.
  • t_1 is the current time-moment of the transition's firing.
  • t_2 is the current value of the duration of its active state.
  • r is the transition's condition, determining which tokens will transfer from the transition's inputs to its outputs. The parameter has the form of an index matrix:
     r = 
\begin{array}{c|c c c c c}  & l''_1 & ... & l''_j & ... & l''_n \\
\hline
l'_1 &  &  &  &  & \\
...  &  &  &  &  & \\
l'_i &  &  & r_{i,j}  &  & \\
...  &  &  &  &  & \\
l'_m &  &  &  &  & \\
\end{array}
    where r_{i,j} are predicates, 1 \le i \le m, 1 \le j \le n
  • M is the index matrix of the capacities of the transition's arcs:
     M = 
\begin{array}{c|c c c c c}  & l''_1 & ... & l''_j & ... & l''_n \\
\hline
l'_1 &  &  &  &  & \\
...  &  &  &  &  & \\
l'_i &  &  & M_{i,j}  &  & \\
...  &  &  &  &  & \\
l'_m &  &  &  &  & \\
\end{array}
    where M_{i,j} \ge 0 are natural numbers or \infty, 1 \le i \le m, 1 \le j \le n
  • \Box is called transition's type, an object having a form similar to a Boolean expression. It may contain as variables the symbols that serve as labels for transition's input places, and it is an expression constructed of variables and the Boolean connectives \land and \lor determining the following conditions:
    \land(l_{i_1}, l_{i_2},...,l_{i_u}) - each of the places l_{i_1}, l_{i_2},...,l_{i_u} must contain at least one token,
    \lor(l_{i_1}, l_{i_2},...,l_{i_u}) - there must be at least one token in the set of places l_{i_1}, l_{i_2},...,l_{i_u} where \lbrace l_{i_1}, l_{i_2},...,l_{i_u} \rbrace \subset L'
    When the value of a type (calculated as a Boolean expression) is "true", the transition can become active, otherwise it cannot.

References