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

Communication is becoming one of the central elements in software development. As a potential typed foundation for structured communication-centred programming, session types have been studied over the last decade for a wide range of process calculi and programming languages, focussing on binary (two-party) sessions. This work extends the foregoing theories of binary session types to multiparty, asynchronous sessions, which often arise in practical communication-centred applications. Presented as a typed calculus for mobile processes, the theory introduces a new notion of types in which interactions involving multiple peers are directly abstracted as a global scenario. Global types retain a friendly type syntax of binary session types while capturing complex causal chains of multiparty asynchronous interactions. A global type plays the role of a shared agreement among communication peers, and is used as a basis of efficient type checking through its projection onto individual peers. The fundamental properties of the session type discipline such as communication safety, progress and session fidelity are established for generaln-party asynchronous interactions.

http://www.sti.uniurb.it/events/sfm15mp/slides/yoshida.pdf

Multiparty asynchronous session types

The π-Calculus: A theory of mobile processes by Davide Sangiorgi and David Walker Formal methods have formed the foundation of Computer Science since its inception. Although, initially these formal methods dealt with processes and systems on an individual basis, the paradigm has shifted with the dawn of the age of computer networks. When dealing with systems with interconnected, communicating, dependent, cooperative, and competitive components, the older outlook of analyzing and developing singular systems—and the tools that went with it—were hardly suitable. This led to the development of theories and tools that would support the new paradigm. On the tools end, the development has been widespread and satisfactory: programming languages, development frameworks, databases, and even end-user software products such as word processors, have gained network-awareness. However on the theoretical end, the development has been far less satisfactory. The major work was done by Robin Milner, Joachim Parrow, and David Walker who developed the formalism known as π-calculus in 1989. π-calculus is a process calculus that treats communication between its components as the basic form of computation. It has been quite successful as a foundation of several other calculi in the field and as Milner puts it, it has become common to express ideas about interactions and mobility in variants of the calculus. Introduction The current book serves as a comprehensive reference to π-calculus. Besides Milner's own book on the subject, this is the only other book-length publication on the topic. In many ways, it is much more comprehensive than Milner's: a much wider area of topics are dealt with and in more detail as well. Contents The book is split into seven part. The first part presents the basic theory of π-calculus. However, basic does not mean concise: every topic is discussed in great detail. The section on bisimulation is particularly intensive and provides several insights about the motivation for the theory. Part two discusses several variants of the original calculus. By varying several characteristics of the calculus, such as whether a process can communicate with more than processes at a time, we can obtain these variants. A number of interesting properties of the language are studied by the other when discussing these variants. As can be understood from the title, the calculus' contribution to analyzing mobile processes is a major topic, and it is dealt with extensively starting from part three. The basics are introduced by the way of a sophisticated typing system whose application in speciying complex processes is presented in part four. Part five looks at higher-order π-calculus in which composed systems are considered as first-class citizens. Part six is one of the best in the book and discusses the relation between π-calculus and lambda-calculus, which is an older and more basic calculus. Finally part seven shows how π-calculus can be employed in studying practical, modern software engineering concepts such as object-oriented programming. Impressions One of my disappointments with this book is in how often the reader is left perplexed with some of the theoretical developments, specially in part three. π-calculus is a complicated topic, even for the graduate student audience to which this book is directed, and the author would have done much better by reducing the number of topics and instead focusing on more lucid and detailed explanations. There are several experimental digressions throughout the book, which although interesting, take away from some of the momentum of sequential study. For example, topics such as comparison and encoding of one language to another could be easily moved to a separate section in order to make the content more suitable for self-study. Another issue is the little effort towards making the connection from the theoretical to the practical. The main reason why formal methods have not been adopted in mainstream software development pracitces is that often it is unclear to developers how formalisms can contribute towards the software engineering process. The book would have served its purpose much better if it had spent part of eah chapter discussing the practical application of that chapter's content. For example, congruence checking and bisimulation can be incredbily exciting topics for programmers to learn if they can see practical applications of such powerful techniques. Beyond the above criticism, the book is absolutely indispensible to students and researchers in the field of formal methods. Currently it serves as the primary reference for anyone who wishes to learn the various aspects of π-calculus in detail. Raheel Ahmad

The Ï-Calculus: A theory of mobile processes

Communication is a central elements in software development. As a potential typed foundation for structured communication-centered programming, session types have been studied over the past decade for a wide range of process calculi and programming languages, focusing on binary (two-party) sessions. This work extends the foregoing theories of binary session types to multiparty, asynchronous sessions, which often arise in practical communication-centered applications. Presented as a typed calculus for mobile processes, the theory introduces a new notion of types in which interactions involving multiple peers are directly abstracted as a global scenario. Global types retain the friendly type syntax of binary session types while specifying dependencies and capturing complex causal chains of multiparty asynchronous interactions. A global type plays the role of a shared agreement among communication peers and is used as a basis of efficient type-checking through its projection onto individual peers. The fundamental properties of the session type discipline, such as communication safety, progress, and session fidelity, are established for general n-party asynchronous interactions.

Multiparty Asynchronous Session Types

We propose a formalisation of the notion of transaction, using a variant of CCS, RCCS, that distinguishes reversible and irreversible actions, and incorporates a distributed backtrack mechanism. Any weakly correct implementation of a transaction in CCS, once embedded in RCCS, automatically obtains a correct one. We show examples where this method allows for a more concise implementation and a simpler proof of correctness.

Transactions in RCCS

A key aspect when aggregating business processes and web services is to assure transactional properties of process executions. Since transactions in this context may require long periods of time to complete, traditional mechanisms for guaranteeing atomicity are not always appropriate. Generally the concept of long running transactions relies on a weaker notion of atomicity based on compensations. For this reason, programming languages for service composition cannot leave out two key aspects: compensations, i.e. ad hoc activities that can undo the effects of a process that fails to complete, and transactional boundaries to delimit the scope of a transactional flow. This paper presents a hierarchy of transactional calculi with increasing expressiveness. We start from a very small language in which activities can only be composed sequentially. Then, we progressively introduce parallel composition, nesting, programmable compensations and exception handling. A running example illustrates the main features of each calculus in the hierarchy.

Theoretical foundations for compensations in flow composition languages

Web services composition is an emerging paradigm for the integration of long running business processes, attracting the interest of both Industry, in terms of XML-based standards for business description, and Academy, exploiting process description languages. The key challenging aspects to model are orchestration workflows, choreography of exchanged messages, fault handling, and transactional integrity with compensation mechanisms. Few recent proposals attempted to mitigate the explosion of XML-constructs in ad hoc standards by a careful selection of a small set of primitives related to the above aspects. This papers clarifies analogies and differences between two such recent process description languages: one based on interleaving trace semantics and the other on concurrent traces. We take advantage of their comparison to characterise and relate four different coordination policies for compensating parallel processes. Such policies differ on the way in which the abort of a process influences the execution of sibling processes, and whether compensation is distributed or centralised.

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Comparing two approaches to compensable flow composition

In global computing applications the availability of a mechanism for some form of committed choice can be useful, and sometimes necessary. It can conveniently handle, e.g., distributed agreements and negotiations with nested choice points. We propose a linguistic extension of the Join calculus for programming nested commits, called Committed Join (cJoin). It provides primitives for explicit abort programmable compensations and interactions between negotiations. We give the operational semantics of cJoin in the reflexive CHAM style. Then we discuss its expressiveness on the basis of a few examples and encodings. Finally, we provide a big-step semantics for cJoin processes that can be typed as shallow and we show that shallow processes are serializable.

/pdf/nested-commits-for-mobile-calculi-extending-join-xgzxnuyfwk.pdf

Nested Commits For Mobile Calculi: Extending Join

Service oriented applications feature interactions among several participants over the network. Mechanisms such as correlation sets and two-party sessions have been proposed in the literature to separate messages sent to different instances of the same service. This paper presents a process calculus featuring dynamically evolving multiparty sessions to model interactions that spread over several participants. The calculus also provides primitives for service definition/invocation and for structured communication in order to highlight the interactions among the different concepts. Several examples from the SOC area show the suitability of our approach.

Multiparty sessions in SOC

A quite flourishing research thread in the recent literature on component-based system is concerned with the algebraic properties of various kinds of connectors for defining well-engineered systems In a recent paper, an algebra of stateless connectors was presented that consists of five kinds of basic connectors, plus their duals The connectors can be composed in series or in parallel and employing a simple 1-state buffer they can model the coordination language Reo Pawel Sobocinski employed essentially the same stateful extension of connector algebra to provide semantics-preserving mutual encoding with some sort of elementary Petri nets with boundaries In this paper we show how the tile model can be used to extend Sobocinski's approach to deal with P/T nets, thus paving the way towards more expressive connector models

Hernán Melgratti

Papers

Theoretical foundations for compensations in flow composition languages

Comparing two approaches to compensable flow composition

Nested Commits For Mobile Calculi: Extending Join

Multiparty sessions in SOC

A connector algebra for P/T nets interactions