N. Busi and G.M. Pinna. Non-sequential semantics for contextual P/T nets. In Proceedings of 17th Int. Conf. on Applications and Theory of Petri Nets, pages 113-132, June 1996. Osaka.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....the four slot algorithm presented in [Sim90b] using the unfolding technique. They con rm that unfolding can support self loops but the combination of concurrency and con ict cause the technique to lose its eciency. Their solution to this eciency problem was to introduce contextualnets [BP96] This change resulted in an unfolding of 1299 transition instances for the contextual net, in contrast to the Petri net unfolding which could not be built due to size ( 3000 transition instances) Their results claim con rmation that the four slot maintains data coherence. The data freshness ....

N. Busi and G.M. Pinna. Non-sequential semantics for contextual P/T nets. In Proceedings of 17th Int. Conf. on Applications and Theory of Petri Nets, pages 113-132, June 1996. Osaka.

....to the classical model concerns a class of nets where transitions are able to check for the presence of a token in a place without actually consuming it. While the possibility of sensing for both presence and absence of a token yields very expressive nets equipped also with inhibitory arcs [14, 7, 4, 5], in the paper we focus our attention to nets extended with read arcs only, generically referred to as contextual nets, which have a richer theory and refer to several well tailored applications. In fact, important constructions on ordinary nets can be extended to nets with read arcs, like those ....

N. Busi and M. Pinna. Non-sequential semantics for contextual P/T nets. In J. Billington and W. Reisig, editors, Applications and Theory of Petri Nets 1996, volume 1091 of LNCS. Springer Verlag, 1996.

....paper [18] for an extensive discussion on the usefulness of category theory in computer science. Relation with deterministic processes. The problem of providing a truly concurrent semantics for contextual nets based on (deterministic) processes has been faced by various authors (see, e.g. [28, 17, 19, 9, 36, 38]) Each deterministic process of a contextual net records the events occurring in a single computation of the net and the relationships existing between such events. Clearly, since the unfolding of a net is essentially a nondeterministic process that completely describes the behaviour of the net, ....

N. Busi and G. M. Pinna. Non Sequential Semantics for Contextual P/T Nets. In Application and Theory of Petri Nets, volume 1091 of LNCS, pages 113-132. Springer Verlag, 1996.

....that are indexed by the places) Also several unfolding semantics (see e.g. 36,24] have been proposed that give a denotational interpretation of the interplay between concurrency, causality and nondeterminism. For contextual nets both the process and the unfolding approaches have been studied [27,8,9,2,1], giving a satisfactory understanding of the computational model via the introduction of asymmetric event structures. The algebraic approach, however, has been pursued only in a recent paper by Gadducci and Montanari [16] using matchshare categories. Their basic idea is that, together with ....

N. Busi and M. Pinna. Non sequential semantics for contextual P/T nets. In Application and Theory of Petri Nets, vol. 1091 of Lect. Notes in Comput. Sci., pp. 113--132. Springer, 1996.

....the above nets and introduced operations on these characteristics that made the correspondence between processes and their characteristics a homomorphism. In the present paper we extend the definitions and results of [DMM 89] and [Wnk 97] to contextual nets similar to those in [MR 95] cf. also [BP 96] and [Ris 94] Contextual nets are models of concurrent systems with context dependent actions. A contextual net is shown in figure 1. Circles represent places in which some resources, called tokens, may reside. Boxes represent actions, called transitions. A transition consumes tokens from some ....

Busi, N., Pinna, G. M., Non Sequential Semantics for Contextual P/T Nets, in the Proceedings of 17th Int. Conf. "Application and Theory of Petri Nets", Osaka, Japan, J. Billington and W. Reisig (Eds.), Springer LNCS 1091, 1996, pp.113-132

....in the proceedings of MFCS 97. coexisiting tokens, and each slice (maximal set of unordered conditions) is a reachable marking of N ; each reachable marking is a slice of some process and each step is a set of unordered events. Recently, Petri nets with read arcs have found considerable interest [CH93, JK95, MR95, BG95, BP96]; read arcs as the lines from s in Figure 1 describe reading without consuming, e.g. reading in a database; consequently, a and b in N 1 can occur concurrently. In ordinary nets, loops (arcs from a to s and from s to a and similarly for b) would be used instead, which describe a ....

....e.g. reading in a database; consequently, a and b in N 1 can occur concurrently. In ordinary nets, loops (arcs from a to s and from s to a and similarly for b) would be used instead, which describe a destructive read and rewrite and do not allow concurrency; this is certainly often not adequate. [MR95, JK95, BP96] define processes of nets with read arcs and generalize some of the results listed above, taking step sequences as observations. Whereas in Figure 1 [MR95, BP96] allow a step fa; bg only for N 1 , JK95] allows this step also for N 2 and N 3 ; the reason is that [JK95] views these nets as ....

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N. Busi and M. Pinna. Non-sequential semantics for contextual P/T-nets. In J. Billington and W. Reisig, editors, Applications and Theory of Petri Nets 1996, Lect. Notes Comp. Sci. 1091, 113--132. Springer, 1996.

....and this makes a solution of the MUTEX problem impossible. Read arcs are quite old, but they have found some more attention only recently: CH93] discusses a step semantics for nets with read arcs, MR95] defines net processes (the classical partial order semantics for Petri nets) for them, and in [BP96] this definition (essentially) is extended to nets that also have inhibitor arcs. In these read0 write1 write0 write1 write0 read1 read1 read0 0 1 Figure 12 approaches, a net with read arcs can be translated to an equivalent net without, i.e. read arcs do not have any additional expressivity. ....

N. Busi and M. Pinna. Non-sequential semantics for contextual P/T-nets. In J. Billington and W. Reisig, editors, Applications and Theory of Petri Nets 1996, Lect. Notes Comp. Sci. 1091, 113--132. Springer, 1996.

....with the use of SGs (see an example below) The root of this problem, informally, is in the different semantic interpretations applied to self loops in ordinary PNs and in contextual nets. This appears to be critical, from the size point of view, for the partial order (or non sequential) semantics [1]. Indeed, the PN unfolding is a partial order technique which proves to be efficient for a large class of PN models it can keep concurrency in its natural, non interleaving , form. Unfortunately, the classical partial order semantics, underlying the existing unfolding methods, loses it ....

....the latter can fire completely independently of each other. This paper proposes a new STG unfolding algorithm, to allow explicit contextual arcs in the underlying PN. This algorithm may find its theoretical justification in the work on non sequential semantics of contextual nets by Busi and Pinna [1]. We have implemented this algorithm in our asynchronous circuit verification synthesis tool PUNT, and applied it to a number of characteristic examples of models with contextual arcs. Those examples include the verification of asynchronous circuits for hazard freedom (checking output signal p1 ....

[Article contains additional citation context not shown here]

N. Busi and G.M. Pinna. Non-sequential semantics for contextual P/T nets. In Proc. of 17th Int. Conf. on Applications and Theory of Petri Nets, Osaka, pages 113--132, June 1996.

....In this paper we consider marked contextual P T nets (shortly c nets) that following the lines suggested in [14] for C E systems, add contexts to classical P T nets. The problem of giving a truly concurrent semantics based on (deterministic) processes has been faced by various authors (see, e.g. [9, 14, 4, 19]) Each process of a c net records the events occurring in a single computation of the net and the relations existing between such events. 89: ffl s0 F NaN F NaN fflffl t0 = 89: ffl s F NaN F NaN fflffl t1 t 0 1 # t0 F NaN F NaN fflffl t 00 1 (a) b) Fig. 1. A simple ....

N. Busi and G. M. Pinna. Non Sequential Semantics for Contextual P/T Nets. In Application and Theory of Petri Nets, volume 1091 of LNCS, pages 113--132. Springer Verlag, 1996.

....is defined (and if it is not then the two states become indistinguishable) The third requirement is to assure that the simulation is uniform on an event. 3 Elementary net systems We recall some basic notions on elementary nets [12] extending them with inhibitor arcs (for this notion see [9] and [6]) Definition6. A net is a tuple (B; E; F ) such that B [ E 6= B E = F (B Theta E) E Theta B) and dom(F ) ran(F ) B [ E 3 . 2 The elements of B are called conditions and the elements of E are called events. F is the flow relation. For x 2 B [ E, we define ffl x = fy 2 B ....

N. Busi and G. M. Pinna. Nonsequential semantics for contextual P/T nets. In Application and Theory of Petri Nets 1996, Lecture Notes in Computer Science 1091, pages 113--132, 1996.

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