6,908 research outputs found
Applied Visual Anthropology
We study a new partial order semantics of Petri nets with read arcs, where read arcs model reading without consuming, which is often more adequate than the destructive-read-and-rewrite modelled in ordinary nets. As basic observations we take ST-traces, which are sequences of transition starts and ends. We define processes of our nets and derive two partial orders modelling causality and start precedence. These partial orders are related to observations and system states just as in the ordinary approach the single partial order of a process is related to firing sequences and reachable markings. Our approach also supports a new view of concurrency as captured by steps. 1 Introduction Describing the runs of a concurrent system by sequences of actions ignores the possible concurrency of these actions, which can be important e.g. for judging the temporal efficiency of the system. Alternatively to this so-called interleaving approach, one can take step sequences, where a step consists of si..
Two Algebraic Process Semantics for Contextual Nets
We show that the so-called 'Petri nets are monoids' approach initiated by Meseguer and Montanari can be extended from ordinary place/transition Petri nets to contextual nets by considering suitable non-free monoids of places. The algebraic characterizations of net concurrent computations we provide cover both the collective and the individual token philosophy, uniformly along the two interpretations, and coincide with the classical proposals for place/transition Petri nets in the absence of read-arcs
Algebraic Models for Contextual Nets
We extend the algebraic approach of Meseguer and Montanari from ordinary place/transition Petri nets to contextual nets, covering both the collective and the individual token philosophy uniformly along the two interpretations of net behaviors
Petri nets for systems and synthetic biology
We give a description of a Petri net-based framework for
modelling and analysing biochemical pathways, which uni¯es the qualita-
tive, stochastic and continuous paradigms. Each perspective adds its con-
tribution to the understanding of the system, thus the three approaches
do not compete, but complement each other. We illustrate our approach
by applying it to an extended model of the three stage cascade, which
forms the core of the ERK signal transduction pathway. Consequently
our focus is on transient behaviour analysis. We demonstrate how quali-
tative descriptions are abstractions over stochastic or continuous descrip-
tions, and show that the stochastic and continuous models approximate
each other. Although our framework is based on Petri nets, it can be
applied more widely to other formalisms which are used to model and
analyse biochemical networks
Encoding Higher Level Extensions of Petri Nets in Answer Set Programming
Answering realistic questions about biological systems and pathways similar
to the ones used by text books to test understanding of students about
biological systems is one of our long term research goals. Often these
questions require simulation based reasoning. To answer such questions, we need
formalisms to build pathway models, add extensions, simulate, and reason with
them. We chose Petri Nets and Answer Set Programming (ASP) as suitable
formalisms, since Petri Net models are similar to biological pathway diagrams;
and ASP provides easy extension and strong reasoning abilities. We found that
certain aspects of biological pathways, such as locations and substance types,
cannot be represented succinctly using regular Petri Nets. As a result, we need
higher level constructs like colored tokens. In this paper, we show how Petri
Nets with colored tokens can be encoded in ASP in an intuitive manner, how
additional Petri Net extensions can be added by making small code changes, and
how this work furthers our long term research goals. Our approach can be
adapted to other domains with similar modeling needs
Read Operators and their Expressiveness in Process Algebras
We study two different ways to enhance PAFAS, a process algebra for modelling
asynchronous timed concurrent systems, with non-blocking reading actions. We
first add reading in the form of a read-action prefix operator. This operator
is very flexible, but its somewhat complex semantics requires two types of
transition relations. We also present a read-set prefix operator with a simpler
semantics, but with syntactic restrictions. We discuss the expressiveness of
read prefixes; in particular, we compare them to read-arcs in Petri nets and
justify the simple semantics of the second variant by showing that its
processes can be translated into processes of the first with timed-bisimilar
behaviour. It is still an open problem whether the first algebra is more
expressive than the second; we give a number of laws that are interesting in
their own right, and can help to find a backward translation.Comment: In Proceedings EXPRESS 2011, arXiv:1108.407
Size-Change Termination as a Contract
Termination is an important but undecidable program property, which has led
to a large body of work on static methods for conservatively predicting or
enforcing termination. One such method is the size-change termination approach
of Lee, Jones, and Ben-Amram, which operates in two phases: (1) abstract
programs into "size-change graphs," and (2) check these graphs for the
size-change property: the existence of paths that lead to infinite decreasing
sequences.
We transpose these two phases with an operational semantics that accounts for
the run-time enforcement of the size-change property, postponing (or entirely
avoiding) program abstraction. This choice has two key consequences: (1)
size-change termination can be checked at run-time and (2) termination can be
rephrased as a safety property analyzed using existing methods for systematic
abstraction.
We formulate run-time size-change checks as contracts in the style of Findler
and Felleisen. The result compliments existing contracts that enforce partial
correctness specifications to obtain contracts for total correctness. Our
approach combines the robustness of the size-change principle for termination
with the precise information available at run-time. It has tunable overhead and
can check for nontermination without the conservativeness necessary in static
checking. To obtain a sound and computable termination analysis, we apply
existing abstract interpretation techniques directly to the operational
semantics, avoiding the need for custom abstractions for termination. The
resulting analyzer is competitive with with existing, purpose-built analyzers
A Formal Framework for Linguistic Annotation
`Linguistic annotation' covers any descriptive or analytic notations applied
to raw language data. The basic data may be in the form of time functions --
audio, video and/or physiological recordings -- or it may be textual. The added
notations may include transcriptions of all sorts (from phonetic features to
discourse structures), part-of-speech and sense tagging, syntactic analysis,
`named entity' identification, co-reference annotation, and so on. While there
are several ongoing efforts to provide formats and tools for such annotations
and to publish annotated linguistic databases, the lack of widely accepted
standards is becoming a critical problem. Proposed standards, to the extent
they exist, have focussed on file formats. This paper focuses instead on the
logical structure of linguistic annotations. We survey a wide variety of
existing annotation formats and demonstrate a common conceptual core, the
annotation graph. This provides a formal framework for constructing,
maintaining and searching linguistic annotations, while remaining consistent
with many alternative data structures and file formats.Comment: 49 page
- …