Wyniki wyszukiwania - Biblioteka Nauki

1

Peter Lauer and COSY

100%

Koutny M.

|

tom Vol. 40, Nr 2,3

103-107

2

Structured Occurrence Nets: A Formalism for Aiding System Failure Prevention and Analysis Techniques

63%

Koutny M. , Randell B.

|

2009

|

tom Vol. 97, nr 1/2

41-91

EN

This paper introduces the concept of a "structured occurrence net", which as its name indicates is based on that of an "occurrence net", a well-established formalism for an abstract record that represents causality and concurrency information concerning a single execution of a system. Structured occurrence nets consist of multiple occurrence nets, associated together by means of various types of relationship, and are intended for recording or predicting, either the actual behaviour of complex systems as they communicate and evolve, or evidence that is being gathered and analysed concerning their alleged past behaviour. We provide a formal basis for the new formalism and show how it can be used to gain better understanding of complex fault-error-failure chains (i) among co-existing communicating systems, (ii) between systems and their sub-systems, and (iii) involving systems that are controlling, creating ormodifying other systems. We then go on to discuss how, with appropriate tools support, perhaps using extended versions of existing tools, structured occurrence nets could form a basis for improved techniques of system failure prevention and analysis.

3

Minimal Regions of ENL-Transition Systems

63%

Koutny M. , Pietkiewicz-Koutny M.

|

tom Vol. 101, nr 1/2

45-58

EN

One of the possible ways of constructing concurrent systems is their automated synthesis from behavioural specifications. In this paper, we look at a particular instance of this approach which aims at constructing GALS (globally asynchronous locally synchronous) systems from specifications given in terms of transition systems with arcs labelled by steps of executed actions. GALS systems are represented by Elementary Net Systems with Localities (ENL-systems), each locality defining a set of co-located actions. The synthesis procedure is based on the regions of transition systems and we provide a number of criteria aimed at generating a minimal set of regions (conditions) of an ENL-system generating a given transition system.

4

Behaviour Abstraction for Communicating Sequential Processes

63%

Koutny M. , Pappalardo G.

|

2001

|

tom Vol. 48, nr 1

21-54

EN

We investigate the notion that a system is an acceptable implementation of another base or target system, in the case that the two systems (or processes) have different interfaces. For instance, the base processes can be thought of as specifications, or ideal processes operating in an error-free environment, while the implementations model their actual realisations, operating in an error-prone environment and possibly employing a variety of fault-tolerant techniques. Using the CSP model, we relate implementations and base systems in terms of their observable behaviours. We obtain two fundamental results, viz. realisability and compositionality. The former ensures that implementations may be put to good use, while the latter guarantees that a target composed of several connected subsystems may be implemented by connecting their respective implementations.

5

Processes of Petri Nets with Range Testing

63%

Kleijn J. , Koutny M.

|

2007

|

tom Vol. 80, nr 1-3

199-219

EN

We are concerned with causality semantics in the executions of Petri nets with range arcs. Range arcs combine (and subsume) the distinctive features of inhibitor and activator arcs, and each such arc provides a means of specifying a range (a finite or infinite interval of non-negative integers) for the number of tokens in a place which makes enabling of a given transition possible. We demonstrate that the existing treatment of causality developed for Petri nets with inhibitor arcs based on structures generalising partial orders can also be applied to nets with range arcs.

6

On causality semantics of nets with priorities

63%

Janicki R. , Koutny M.

|

1999

|

tom Vol. 38, Nr 3

223-255

EN

In the formal treatment of concurrent computing systems, causality and weak causality can be used to provide abstract specifications of the temporal `earlier than' and `not later than' orderings. In this paper we consider relational structures comprising causality and weak causality - called stratified order structures - which can be used to provide a non-sequential semantics of Petri nets with inhibitor arcs. We show that this approach can be extended to nets augmented with priority specifications. In particular, we demonstrate how to derive stratified order structures for such nets by generalising the standard construction of causal partial orders based on occurrence nets

7

Simulation study of delay of medical data transmission in bottleneck network

51%

Mlynek P. , Misurec J. , Koutny M. , Dostal O.

|

tom R. 89, nr 6

93--97

EN

The article deals with the delay of medical data in queues, caused by a bottleneck in the network. Primarily it focuses on the mathematical basis for defining the entrance traffic based on exponential distribution in the Network simulator. In the simulation part a model of input medical imaging data is implemented, and simulations are performed on a network with a bottleneck, when the delay is measurement for different combinations of active input medical imaging sources.

PL

W artykule analizuje się opóźnienie w przepływie danych medycznych spowodowanych obecnością wąskich gardeł sieci. Przeprowadzono szereg symulacji dla różnych rodzajów przesyłu obrazu w projekcie MeDiMed.

8

Overlapped filtered multitone modulation and its optimization on VLIW DSP

51%

Silhavy P. , Krajsa O. , Systel P. , Koutny M.

|

tom R. 87, nr 12a

145-149

EN

In recent years, the multicarrier modulations (MCM) have been applied to wire and wireless transmission systems. MCM enable a nearperfect utilization of the provided frequency band on metallic cables and they also effectively eliminate multipath propagation in terrestrial transmission. They are mainly the implementations called Discrete MultiTone (DMT) and Orthogonal Frequency Division Multiplexing (OFDM). These approaches have also disadvantages, which have led to seeking new approaches to the implementation of the MCM modulation scheme. One of them is the Filtered MultiTone Modulation (FMT). In the article, the channel equalization in overlapped and non-overlapped FMT modulation will be compared. The optimal implementation of FMT on the VLIW DSP will be introduced in the second part.Optimized implementation of filter bank with the help of parallel processing is described, and also frame writing/reading and its synchronization are introduced.

PL

W ostatnich latach, w modulacjach multicarrier (MCM) zostały zastosowane systemy transmisji przewodowej i bezprzewodowej. MCM umożliwiają niemal perfekcyjne wykorzystanie pasma częstotliwości przewidziane w kablach a również skutecznie wyeliminować wielodrogowość w transmisji naziemnej. Są to przede wszystkim implementacje o nazwie Discrete wielotonowy (DMT) i Orthogonal Frequency Division Multiplexing (OFDM). Metody te mają także wady, które doprowadziły do poszukiwania nowych sposobów podejściacia do wdrożenia systemu modulacji MCM. Jednym z nich jest filtrowane wielotonowe modulacji (FMT). W drugiej częścici artykułu została opisana optymalna implementacja modulacji FMT. Wykorzystano bank filtrów z równoległym przetwarzaniem, oraz odpowiednie ramki zapisu/odczytu oraz synchronizacji.

9

Invariant Structures and Dependence Relations

51%

Janicki R. , Kleijn J. , Koutny M. , Mikulski Ł.

|

tom Vol. 155, nr 1/2

1--29

EN

A step trace is an equivalence class of step sequences which can be thought of as different observations of the same underlying concurrent history. Equivalence is determined on basis of a step alphabet that describes the relations between events in terms of potential simultaneity and sequentialisability. Step traces cannot be represented by standard partial orders, but require so-called invariant structures, extended order structures that capture the phenomena of mutual exclusion and weak causality. In this paper, we present an effective way of deciding whether an invariant structure represents a step trace over a given step alphabet. We also describe a method by which one can check whether a given invariant structure can represent a step trace over any step alphabet. Moreover, if the answer is positive, the method provides a suitable step alphabet.

10

Reversing Transitions in Bounded Petri Nets

45%

Barylska K. , Erofeev E. , Koutny M. , Mikulski Ł. , Piątkowski M.

|

tom Vol. 157, nr 4

341--357

EN

Reversible computation deals with mechanisms for undoing the effects of actions executed by a dynamic system. This paper is concerned with reversibility in the context of Petri nets which are a general formal model of concurrent systems. A key construction we investigate amounts to adding ‘reverse’ versions of selected net transitions. Such a static modification can severely impact on the behaviour of the system, e.g., the problem of establishing whether the modified net has the same states as the original one is undecidable. We therefore concentrate on nets with finite state spaces and show, in particular, that every transition in such nets can be reversed using a suitable set of new transitions.

11

Persistent and Nonviolent Steps and the Design of GALS Systems

38%

Fernandes J. , Koutny M. , Mikulski Ł. , Pietkiewicz-Koutny M. , Sokolov D. , Yakovlev A.

|

tom Vol. 137, nr 1

143--170

EN

A concurrent system is persistent if throughout its operation no activity which became enabled can subsequently be prevented from being executed by any other activity. This is often a highly desirable (or even necessary) property; in particular, if the system is to be implemented in hardware. Over the past 40 years, persistence has been investigated and applied in practical implementations assuming that each activity is a single atomic action which can be represented, for example, by a single transition of a Petri net. In this paper we investigate the behaviour of GALS (Globally Asynchronous Locally Synchronous) systems in the context of VLSI circuits. The specification of a system is given in the form of a Petri net. Our aim is to re-design the system to optimise signal management, by grouping together concurrent events. Looking at the concurrent reachability graph of the given Petri net, we are interested in discovering events that appear in ‘bundles’, so that they all can be executed in a single clock tick. The best candidates for bundles are sets of events that appear and re-appear over and over again in the same configurations, forming ‘persistent’ sets of events. Persistence was considered so far only in the context of sequential semantics. In this paper, we move to the realm of step based execution and consider not only steps which are persistent and cannot be disabled by other steps, but also steps which are nonviolent and cannot disable other steps. We then introduce a formal definition of a bundle and propose an algorithm to prune the behaviour of a system, so that only bundled steps remain. The pruned reachability graph represents the behaviour of a re-engineered system, which in turn can be implemented in a new Petri net using the standard techniques of net synthesis. The proposed algorithm prunes reachability graphs of persistent and safe nets leaving bundles that represent maximally concurrent steps.