物件導向軟體之架構(Object-Oriented Software Construction)探討

[서평]「Component Software」 - Beyond Object-Oriented Programming -

A new class of models, formalisms and mechanisms has recently evolved for describing concurrent and distributed computations based on the concept of ``coordination''''. The purpose of a coordination model and associated language is to provide a means of integrating a number of possibly heterogeneous components together, by interfacing with each component in such a way that the collective set forms a single application that can execute on and take advantage of parallel and distributed systems. In this chapter we initially define and present in sufficient detail the fundamental concepts of what constitutes a coordination model or language. We then go on to classify these models and languages as either ``data-driven'''' or ``control-driven'''' (also called ``process-'''' or ``task-oriented''''). Next, the main existing coordination models and languages are described in sufficient detail to let the reader appreciate their features and put them into perspective with respect to each other. The chapter ends with a discussion comparing the various models and some conclusions.

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Coordination models and languages

A super-peer is a node in a peer-to-peer network that operates both as a server to a set of clients, and as an equal in a network of super-peers. Super-peer networks strike a balance between the efficiency of centralized search, and the autonomy, load balancing and robustness to attacks provided by distributed search. Furthermore, they take advantage of the heterogeneity of capabilities (e.g., bandwidth, processing power) across peers, which recent studies have shown to be enormous. Hence, new and old P2P systems like KaZaA and Gnutella are adopting super-peers in their design. Despite their growing popularity, the behavior of super-peer networks is not well understood. For example, what are the potential drawbacks of super-peer networks? How can super-peers be made more reliable? How many clients should a super-peer take on to maximize efficiency? we examine super-peer networks in detail, gaming an understanding of their fundamental characteristics and performance tradeoffs. We also present practical guidelines and a general procedure for the design of an efficient super-peer network.

Designing an Super-Peer Network

All one needs to know about fog computing and related edge computing paradigms: A complete survey

We present a model for distributed logic programming based on ANDparallelism and on explicit message-passing primitives. The communication mechanism is inspired by Milner's CCS [31]. First, a simple calculus of communicating sequential logic processes is defined to formally introduce this notion of communication in a logic programming setting. Then, the definition of the language is completed by extending the calculus with an alternative command, as well as with mechanisms for the dynamic creation of AND-parallel processes. The resulting language is a variant of Distributed Logic defined by Monteiro [33]. The second part of the paper focuses on the study of the semantics of the language. We define a model-theoretic semantics by providing the various goal composition operators and the communication primitives with a clear logical meaning. On the other hand, an operational semantics is given in terms of the distributed model of Petri nets. The latter characterization is shown to provide several insights on the programming language, such as the ability of capturing fairness and liveness properties. The study of the semantics terminates with the proof of the equivalence (soundness and completeness) between the model-theoretic and the operational semantics.

Distributed Logic Programming

Fault-aware management protocols permit modelling the management of application components (including potential faults) and analysing the management behaviour of a multi-component application The analysis is driven by the application topology, and it assumes many-to-1 dependencies among application components, ie each requirement of a component can be satisfied by exactly one other component

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Modelling the Dynamic Reconfiguration of Application Topologies, Faults Included

Predicting the QoS of a service orchestration is not easy because of the a priori undetermined behaviour of invoked services, and because of the non-determinism (alternatives, unbounded iterations, fault handling) and complex structure (dependencies, correlations) of the workflow defining a service orchestration. In this paper we illustrate the practical usefulness of a probabilistic analyser of service orchestrations (PASO) by showing how it can be fruitfully exploited to predict the QoS of service orchestrations.

Automated Prediction of the QoS of Service Orchestrations: PASO at Work

Modern enterprise applications integrate multiple interdependent software components, whose management must be suitably coordinated. This must be done by taking into account all inter-component dependencies, the faults potentially affecting them, and the fact that each component can be horizontally scaled, i.e., that multiple instances of each component can be spawned or destroyed, depending on application needs. In this article, we introduce a novel solution for suitably modelling and analysing the replica- and fault-aware management of multi-component applications, based on topology graphs and management protocols. More precisely, we first introduce a compositional model of the management behaviour of the (possibly multiple) instances of the components forming an application, faults included. We then show how this model enables automating various useful analyses, from checking the validity of management plans to automatically determining management plans allowing the instance of an application to reach and maintain a desired target configuration.

Modelling and Analysing Replica- and Fault-aware Management of Horizontally Scalable Applications

Trans-cloud applications consist of multiple interacting components deployed across different cloud providers and at different service layers (IaaS and PaaS). In such complex deployment scenarios, fault handling and recovery need to deal with heterogeneous cloud offerings and to take into account inter-component dependencies. We propose a methodology for self-healing trans-cloud applications from failures occurring in application components or in the cloud services hosting them, both during deployment and while they are being operated. The proposed methodology enables reducing the time application components rely on faulted services, hence residing in “unstable” states where they can suddenly fail in cascade or exhibit erroneous behaviour. We also present an open-source prototype illustrating the feasibility of our proposal, which we have exploited to carry out an extensive evaluation based on controlled experiments and monkey testing.

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Antonio Brogi

Papers

Distributed Logic Programming

Modelling the Dynamic Reconfiguration of Application Topologies, Faults Included

Automated Prediction of the QoS of Service Orchestrations: PASO at Work

Modelling and Analysing Replica- and Fault-aware Management of Horizontally Scalable Applications

Self-healing trans-cloud applications