Abstract
In the paper, we study a family of testing equivalences in interleaving, partial-order semantics, and combined semantics in the context of safe time Petri nets (elementary net systems whose transitions are labeled with time firing intervals, can fire only if their lower time bounds are attained, and are forced to fire when their upper time bounds are reached). For this purpose, the following three representations of behavior of safe time Petri nets are developed: sequences of firings of net transitions, which represent interleaving semantics; time causal processes, from which partial orders are derived; and time causal tree, whose nodes are sequences of transition firings and arcs are labeled by information about partial orders. We establish relationships between these equivalences and show that semantics of time causal processes and time causal trees coincide.
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Notes
For convenience of subsequent definitions, we do not use the classical definition: a transition \(t \in T\) is enabled at a marking M if \(^{ \bullet }t \subseteq M\) and \(M \cap {{t}^{ \bullet }} = \emptyset \). The second requirement will be introduced in the definition of the contact-free property.
Note that, if the base Petri net N is contact-free, then the time Petri net \(\mathcal{T}\mathcal{N}\) is also contact-free, but the converse is not true.
The time-progressive property guarantees correctness of the modified definition of the contact-free property.
A (labeled overAct) time partially ordered set (poset) is a tuple \(\eta = (X, \preccurlyeq ,\lambda ,\tau )\) consisting of a finite set of elements X; reflexive, asymmetric, and transitive relation \( \preccurlyeq \); a labeling function λ: \(X\, \to \,Act\); and a time function \(\tau {\kern 1pt} :\;X \to T\) such that \(e\, \preccurlyeq \,e'\, \Rightarrow \,\tau (e)\, \leqslant \,\tau (e')\). Let \(\tau (\eta ) = \max\{ \tau (x)\,|\,x \in X\} \).
Two time posets \(\eta = (X, \preccurlyeq ,\lambda ,\tau )\) and \(\eta ' = (X', \preccurlyeq {\kern 1pt} ',\lambda ',\tau ')\) are isomorphic (denoted as \(\eta \simeq \eta '\)) if there exists a bijection \(\beta {\kern 1pt} :\;X \to X'\) such that (a) \(x \preccurlyeq y \Leftrightarrow \beta (x) \preccurlyeq {\kern 1pt} '\,\beta (y)\) for all \(x,y \in X\) and (b) \(\lambda (x) = \lambda '(\beta (x))\) and \(\tau (x) = \tau '(\beta (x))\) for all \(x \in X\).
We define \(path(\epsilon ) = \epsilon \). Note that, in a \(TCT(\mathcal{T}\mathcal{N})\), for any node \(\sigma \in \mathcal{F}\mathcal{S}(\mathcal{T}\mathcal{N})\), there exists a path from the root to a node \(\sigma \).
A time poset \(\eta = (X, \preccurlyeq ,\lambda ,\tau )\) is called prefix of a time poset \(\eta ' = (X', \preccurlyeq ',\lambda ',\tau ')\) (denoted as \(\eta \prec \cdot \eta '\)) if \(X \subseteq X'\), \(X{{'\backslash }}X = \{ x\} \), \( \preccurlyeq = \preccurlyeq ' \cap (X \times X)\), \(\lambda = \lambda '{{{\text{|}}}_{X}}\), \(\tau = \tau '{{{\text{|}}}_{X}}\), and x is the greatest with respect to \( \preccurlyeq '\) element of \(X'\)
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Bozhenkova, E.N., Virbitskaite, I.B. Testing Equivalences of Time Petri Nets. Program Comput Soft 46, 251–260 (2020). https://doi.org/10.1134/S0361768820040040
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DOI: https://doi.org/10.1134/S0361768820040040