U. Montanari and F. Rossi (1995), Contextual Nets. Acta Informatica 32, 545--596, Springer-Verlag.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....have been considered in the literature that either increase the expressive power or give a better representation of existing phenomena. This paper focuses on extending the Petri nets are monoids approach to contextual nets, also known as nets with read arcs, or condition arcs, or testarcs [10,27,19,35]. The motivating idea behind read arcs is that of reading resources without consuming them, thus providing a way of modeling multiple concurrent accesses to the same resource. Using ordinary PT nets such readings must be rendered 2 ######## ## a ######## # # # # # # # # c ....

....and N 3 in Figure 1, taken from [35] As usual, places are represented by circles, tokens by black bullets, transitions by boxes, pre and post sets by directed weighted arcs, and contexts by undirected weighted arcs, with unary weights always omitted. According to the semantic interpretation of [27], the transitions t 0 and t 1 can fire concurrently in N 1 , but neither in N 2 nor in N 3 , since the basic assumption is that a token cannot be read and consumed in the same step. In [19] instead, the concurrent step is allowed for all three nets, the basic assumption being that t 0 and t 1 ....

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U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545--596, 1995.

....subsystems. Several extensions of the basic net paradigm have been considered in the literature that either increase the expressive power or give a better representation of existing phenomena. This paper focuses on contextual nets, also known as nets with read arcs, or condition arcs, or test arcs [4,13,8,21]. The underlying idea is that of reading resources without consuming them, thus providing a way of modeling multiple concurrent accesses to the same resource. With ordinary pt nets such readings must be rendered as self loops, and this imposes an unfortunate sequentialization of concurrent ....

....us consider the nets N 1 , N 2 and N 3 in Figure 1 taken from [21] As usual, places are represented by circles, tokens by black bullets, transitions by boxes, pre and post sets by directed weighted arcs, and contexts by undirected weighted arcs, with unary weights always omitted. According to [13], the transitions t 0 and t 1 can re concurrently in N 1 , but neither in N 2 nor in N 3 , since the basic assumption is that a token cannot be read and consumed in the same step. In [8] instead, the concurrent step is allowed for all three nets, the basic assumption being that t 0 and t 1 can ....

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U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545-596, 1995.

.... is equivalent to history preserving bisimulation defined on nonsequential processes; then we develop a conservative extension of the causal semantics to contextual P T nets (i.e. nets with positive and negative context conditions) and we prove this one to be finer than step semantics, proposed in [8]. 1 Introduction Place Transition nets [9] are a well known model used to describe concurrent systems. Usually a true concurrent semantics for these nets is provided by means of processes [4] then, to take into account also the branching structure of systems, the history preserving bisimulation ....

....turns out to be as discriminating as history preserving bisimulation, hence no information is lost with respect to the one available in the process based semantics. Note that concurrency is still defined as absence of causal dependency. P T nets have been extended by adding contextual information [5, 8]: besides producing and consuming tokens, a transition needs to test for absence and or presence of tokens in some places. The interest for a true concurrent semantics for contextual nets arises from some recent proposals of net semantics for process algebras with evolving connection structure, ....

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U. Montanari, F. Rossi "Contextual Nets", Acta Informatica, to appear.

.... test for presence and absence of tokens, besides the usual flow relation, has grown, mainly due to the use of contextual nets to give a net semantics to the calculus ( 8] studied in [2] or to model the concurrent access to shared data [14, 4] or to their relation with constraint programming [9], or to model priorities [7] Quite clearly contextual Petri nets give a faithful and simpler representation of real systems, for instance timeouts can be modeled just requiring that the various activities (that may be independent to each other) test for the presence of a token in a certain place ....

....are used to forbid certain executions (as in the case of priorities) In this paper we propose a non sequential semantics for contextual P T net that keeps apart causal dependencies, positive context dependencies and negative context dependencies. We define a contextual occurrence net following [9], i.e. representing positive contexts as contextual arcs, as they state a positive depen dency, but where negative contexts are represented via a labeling function. To such a net it is still possible to associate a partial order representing the causal dependencies and the positive contexts ....

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U. Montanari, F. Rossi "Contextual Nets", Acta Informatica 36, 545-596, 1995.

....graph associated to the net for calculus tightly corresponds to its early interleaving transition system. As far as non interleaving semantics are concerned, we observe that nets with inhibitor arcs have not been deeply studied: only some contrasting proposals are reported in the literature [14, 18]. We adapt one of these [18] to P T nets which is suited for our aims, hence providing calculus with a multistep semantics (new to the best of our knowledge) Finally, we present a causal semantics for P T nets with inhibitor arcs; the induced causal semantics for calculus is compared with ....

.... calculus tightly corresponds to its early interleaving transition system. As far as non interleaving semantics are concerned, we observe that nets with inhibitor arcs have not been deeply studied: only some contrasting proposals are reported in the literature [14, 18] We adapt one of these [18] to P T nets which is suited for our aims, hence providing calculus with a multistep semantics (new to the best of our knowledge) Finally, we present a causal semantics for P T nets with inhibitor arcs; the induced causal semantics for calculus is compared with those recently appeared in ....

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U. Montanari, F. Rossi "Contextual Nets", Acta Informatica, to appear.

....set of places (Degano et al. 1988) These are sometimes called location oriented net semantics. However, there is another approach, called label oriented, which partly ignores the syntactical structure of terms and is based mainly on information about transition labels (Goltz, 1988; Gorrieri Montanari, 1995). While the former approach has the merit of having been successfully applied to several process algebras, the latter has the merit of producing smaller net representations. The purpose of this paper is to define a new net semantics for EMPA in the label oriented approach. Following the proposal ....

....arcs, helpful in correctly implementing the action type binding and the related mech The Computer Journal, Vol. 38, No. 7, 2 M. Bernardo, N. Busi and R. Gorrieri anism for generating fresh action types. Thus, the semantic model we use is the stochastic version of the class of contextual nets (Montanari Rossi, 1995). Finally, we show that most inhibitor arcs (all, if we restrict to guarded sum) and all the contextual arcs can be safely removed, obtaining an optimised, compact net semantics. The advantages of this new net semantics with respect to the location oriented one are: ffl Nets are no more 1 safe, ....

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Montanari, U., & Rossi, F. 1995. Contextual Nets.

....in a place: to simulate the generation of a new subnet from the firing of a transition in N , the corresponding transition in NM puts an infinite quantity of tokens in the enabling place corresponding to the subnet. We can avoid such a kind of transitions if we extend our model to contextual nets [5], where a transition can read a token from a place without consuming it. For uniformity reasons, in our encoding we add an enabling place also for the initial net and for subnets with an empty set of transitions; we can avoid to add these redundant places, thus obtaining a more compact net. Let ....

U. Montanari, F. Rossi, "Contextual Nets", Acta Informatica 32(6), 1995.

....DiX. As a consequence of Theorem 4.3, we get a net semantics for CCS, too. Let us define the nets we shall use. 5. 1 P T nets with inhibitor arcs We recall simple Place Transition nets without capacities on places (see, e.g. 28] Then, we extend it with the so called inhibitor arcs (see, e.g. [20, 6, 21, 25]) Here we provide a characterization of this model which is convenient for our aims. Definition 5.1 G iven a set S, a finite multiset over S is a function m : S IN such that the set dom(m) fs 2 S j m(s) 6= 0g is finite. The multiplicity of an element s in m is given by the natural number ....

....languages (to the best of our knowledge) Multistep semantics for P T nets with inhibitor arcs have been investigated in [6] where, however, a different notion of P T net (and of concurrent enabling) is considered. Also some nice work on C E nets [28] with inhibitor arcs is reported in [21] and in [25]; we share with the latter the same basic intuition on concurrency: two transitions such that one produces a token in a place of the inhibitor set of the other cannot be performed in one multistep, as they cannot be executed in either order. Future research will be devoted to prove that the net ....

U. Montanari, F. Rossi "Contextual Nets", Acta Informatica, to appear.

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U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545--596, 1995.

No context found.

U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545--596, 1995.

No context found.

U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545--596, 1995.

No context found.

U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545--596, 1995.

....segments that cannot be completed. Finding some general condition for halting the unfolding of zs is an open problem that we leave for future investigations. 5 Zero safe nets and read arcs We now show how to extend the zero safe net paradigm with read arcs, in the style of contextual nets [34]. The idea is to model transitions that can read certain tokens without consuming them, so that multiple readings on the same token can take place concurrently (using ordinary pt nets, the naive way of modeling readings via self loops 8 is not appropriate because the accesses to read tokens are ....

U. Montanari and F. Rossi. Contextual nets. Acta Inform., 32:545-596, 1995.

No context found.

U. Montanari and F. Rossi (1995), Contextual Nets. Acta Informatica 32, 545--596, Springer-Verlag.

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U. Montanari and F. Rossi. Contextual nets. Acta Inf., 32(6):545--596, 1995.

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U. Montanari and F. Rossi (1995), Contextual Nets. Acta Informatica 32, 545--596, Springer-Verlag.

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