Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

A type system is a syntactic method for automatically checking the absence of certain erroneous behaviors by classifying program phrases according to the kinds of values they compute. The study of type systems -- and of programming languages from a type-theoretic perspective -- has important applications in software engineering, language design, high-performance compilers, and security.This text provides a comprehensive introduction both to type systems in computer science and to the basic theory of programming languages. The approach is pragmatic and operational; each new concept is motivated by programming examples and the more theoretical sections are driven by the needs of implementations. Each chapter is accompanied by numerous exercises and solutions, as well as a running implementation, available via the Web. Dependencies between chapters are explicitly identified, allowing readers to choose a variety of paths through the material.The core topics include the untyped lambda-calculus, simple type systems, type reconstruction, universal and existential polymorphism, subtyping, bounded quantification, recursive types, kinds, and type operators. Extended case studies develop a variety of approaches to modeling the features of object-oriented languages.

https://www.seas.upenn.edu/~bcpierce/tapl/contents.pdf

Types and Programming Languages

We provide an extensive overview of existing research in the field of software refactoring. This research is compared and discussed based on a number of different criteria: the refactoring activities that are supported, the specific techniques and formalisms that are used for supporting these activities, the types of software artifacts that are being refactored, the important issues that need to be taken into account when building refactoring tool support, and the effect of refactoring on the software process. A running example is used to explain and illustrate the main concepts.

/pdf/a-survey-of-software-refactoring-kgrdghit3u.pdf

A survey of software refactoring

Journal of the ACM

Handbook of logic in computer science.

We present an event structure semantics for contextual nets, an extension of P/T Petri nets where transitions can check for the presence of tokens without consuming them (read-only operations). A basic role is played by asymmetric event structures, a generalization of Winskel's prime event structures where symmetric conflict is replaced by a relation modelling asymmetric conflict or weak causality, used to represent a new kind of dependency between events arising in contextual nets. Extending Winskel's seminal work on safe nets, the truly concurrent event-based semantics of contextual nets is given at categorical level via a chain of coreflections leading from the category SW-CN of semi-weighted contextual nets to the category Dom of finitary prime algebraic domains. First an unfolding construction generates from a contextual net a corresponding occurrence contextual net, from where an asymmetric event structure is extracted. Then the configurations of the asymmetric event structure, endowed with a suitable order, are shown to form a finitary prime algebraic domain. We also investigate the relation between the proposed unfolding semantics and several deterministic process semantics for contextual nets in the literature. In particular, the domain obtained via the unfolding is characterized as the collection of the deterministic processes of the net endowed with a kind of prefix ordering. 2001 Elsevier Science.

/pdf/contextual-petri-nets-asymmetric-event-structures-and-1bkeagle2u.pdf

Contextual Petri nets, asymmetric event structures, and processes

In the last 15 years, several research efforts have been directed towards the representation and the analysis of metabolic pathways by using Petri nets. The goal of this paper is twofold. First, we discuss how the knowledge about metabolic pathways can be represented with Petri nets. We point out the main problems that arise in the construction of a Petri net model of a metabolic pathway and we outline some solutions proposed in the literature. Second, we present a comprehensive review of recent research on this topic, in order to assess the maturity of the field and the availability of a methodology for modelling a metabolic pathway by a corresponding Petri net.

/pdf/petri-nets-for-modelling-metabolic-pathways-a-survey-1zuseah8tc.pdf

Petri nets for modelling metabolic pathways: a survey

In this paper we introduce a static analysis technique for graph transformation systems. We present an algorithm which, given a graph transformation system and a start graph, produces a finite structure consisting of a hypergraph decorated with transitions (Petri graph) which can be seen as an approximation of the Winskel style unfolding of the graph transformation system. The fact that any reachable graph has an homomorphic image in the Petri graph and the additional causal information provided by transitions allow us to prove several interesting properties of the original system. As an application of the proposed technique we show how it can be used to verify the absence of deadlocks in an infinite-state Dining Philosophers system.

/pdf/a-static-analysis-technique-for-graph-transformation-systems-2psxy9e0kw.pdf

A Static Analysis Technique for Graph Transformation Systems

Graph grammars (or graph transformation systems), originally introduced as a generalization of string grammars, can be seen as a powerful formalism for the specification of concurrent and distributed systems, which properly extends Petri nets. The idea is that the state of a distributed system can be naturally represented (at a suitable level of abstraction) as a graph and local state transformations can be expressed as production applications. With the aim of consolidating the foundations of the concurrency theory for graph transformation systems, the thesis extends to this more general setting some fundamental approaches to the semantics coming from Petri net theory. More specifically, focusing on the so-called double pushout (dpo) algebraic approach to graph rewriting, the thesis provides graph transformation systems with truly concurrent semantics based on (concatenable) processes and on a Winskel’s style unfolding construction, as well as with more abstract semantics based on event structures and domains. The first part of the thesis studies two generalizations of Petri nets, already known in the literature, which reveal a close relationship with graph transformation systems, namely contextual nets (also called nets with read, activator or test arcs) and inhibitor nets (or nets with inhibitor arcs). Extending Winskel’s seminal work on safe nets, the truly concurrent semantics of contextual nets is given via a chain of coreflections leading from the category of contextual nets to the category of finitary coherent prime algebraic domains. A basic role is played by asymmetric event structures, which generalize prime event structures by allowing a non-symmetric conflict relation. The work is then generalized to inhibitor nets, where, due to the non-monotonicity of the enabling, the causal structure of computations is far more complex, and a new, very general, notion of event structure, called inhibitor event structure, is needed to faithfully describe them. The second part of the thesis, relying on the conceptual basis drawn in the first part, focuses on graph grammars. Inhibitor event structures turn out to be expressive enough to model graph grammar computations, and the theory developed for contextual and inhibitor nets, comprising the unfolding and the (concatenable) process semantics, can be lifted to graph grammars. The developed semantics is shown to to be consistent also with the classical theory of concurrency for dpo graph grammars relying on shift-equivalence.

/pdf/modelling-concurrent-computations-from-contextual-petri-nets-3esdzstsg6.pdf

Modelling Concurrent Computations: from Contextual Petri Nets to Graph Grammars

We propose a technique for the analysis of graph transformation systems based on the construction of finite structures approximating the behaviour of such systems with arbitrary accuracy. Following a classical approach, one can construct a chain of finite under-approximations (k-truncations) of the Winskel's style unfolding of a graph grammar. More interestingly, also a chain of finite over-approximations (k-coverings) of the unfolding can be constructed and both chains converge (in a categorical sense) to the full unfolding. The finite over- and under-approximations can be used to check properties of a graph transformation system, like safety and liveness properties, expressed in (meaningful fragments of) the modal µ-calculus. This is done by embedding our approach in the general framework of abstract interpretation.

/pdf/approximating-the-behaviour-of-graph-transformation-systems-1g2ej0m5xe.pdf

Paolo Baldan

Papers

Contextual Petri nets, asymmetric event structures, and processes

Petri nets for modelling metabolic pathways: a survey

A Static Analysis Technique for Graph Transformation Systems

Modelling Concurrent Computations: from Contextual Petri Nets to Graph Grammars

Approximating the Behaviour of Graph Transformation Systems