A Calculus for Orchestration of Web Services

Service-oriented computing, an emerging paradigm for distributed computing based on the use of services, is calling for the development of tools and techniques to build safe and trustworthy systems, and to analyse their behaviour. Therefore, many researchers have proposed to use process calculi, a cornerstone of current foundational research on specification and analysis of concurrent, reactive, and distributed systems. In this paper, we follow this approach and introduce CWS, a process calculus expressly designed for specifying and combining service-oriented applications, while modelling their dynamic behaviour. We show that CWS can model all the phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, orchestration, deployment, reconfiguration and execution. We illustrate the specification style that CWS supports by means of a large case study from the automotive domain and a number of more specific examples drawn from it

A Logical Verification Methodology for Service-Oriented Computing

We introduce a logical verification methodology for checking behavioural properties of service-oriented computing systems. Service properties are described by means of SocL, a branching-time temporal logic that we have specifically designed to express in an effective way distinctive aspects of services, such as, e.g., acceptance of a request, provision of a response, and correlation among service requests and responses. Our approach allows service properties to be expressed in such a way that they can be independent of service domains and specifications. We show an instantiation of our general methodology that uses the formal language COWS to conveniently specify services and the expressly developed software tool CMC to assist the user in the task of verifying SocL formulae over service specifications. We demonstrate feasibility and effectiveness of our methodology by means of the specification and the analysis of a case study in the automotive domain

Designing and experimenting coordination primitives for service oriented computing

Service Oriented Architecture (SOA) and Web Services (WS) are becoming a widely accepted device for designing and implementing distributed systems. SOAs have given an important contribution to software engineering providing a model where applications are defined by assembling together certain functionalities, called services, possibly provided by remote suppliers. The characterizing issue of SOAs consists of defining common principles to make services accessible and usable regardless their execution context. Nevertheless, the architectural specification is far from giving a complete reference application model on which systems should rely on. The specification just includes principles for achieving interoperability and reusability of services; other aspects are left to the implementing platforms. As a consequence, it is understood how services are specified in isolation and how their functionalities are made available to the requesters, but the definition of languages for describing service composition are far from being widely accepted and reveals to be an impelling challenge. In the last years, several solutions have been proposed for describing aggregated services. However, they often lack a formally defined semantics. Moreover, these solutions are often specific for a platform (e.g. WSs) and are difficult to adapt to other platforms since they rely on low level assumptions that are out of the SOA specifications. This thesis aims at providing new methodologies for implementing the coordination of services. Our framework proposes to be flexible enough to support high level languages and to provide reliable tools for testing correctness of implementation. Our approach relies on a formal model that takes the form of a process calculus specifically designed to deal with services and their coordination. The process calculus has been the main tool driving the specification issues as well the implementation issues. Indeed, it acts as a bridge between the high level specification language and the run-time environment. A distinguished feature of our proposal is that our formal model, i.e. the process calculus, describes distributed processes relying on an event notification mechanism as machinery for interactions. Services are represented by certain components that embody local computations and react to changes of the overall environment in which they are involved. The adoption of event notification results particularly fashionable for tackling service coordination. The principles studied at specification level are from one side understood within a theoretical framework that provides instruments for checking correctness of interaction policies and from the other side offers the core model for implementing and experimenting a programming middleware

A programming system for process coordination in virtual organisations

PhD thesisDistributed business applications are increasingly being constructed by composing them from services provided by various online businesses. Typically, this leads to trading partners coming together to form virtual organizations (VOs). Each member of a VO maintains their autonomy, except with respect to their agreed goals. The structure of the Virtual Organisation may contain one dominant organisation who dictates the method of achieving the goals or the members may be considered peers of equal importance. The goals of VOs can be defined by the shared global business processes they contain. To be able to execute these business processes, VOs require a flexible enactment model as there may be no single ‘owner’ of the business process and therefore no natural place to enact the business processes. One solution is centralised enactment using a trusted third party, but in some cases this may not be acceptable (for instance because of security reasons). This thesis will present a programming system that allows centralised as well as distributed enactment where each organisation enacts part of the business process. To achieve distributed enactment we must address the problem of specifying the business process in a manner that is amenable to distribution. The first contribution of this thesis is the presentation of the Task Model, a set of languages and notations for describing workflows that can be enacted in a centralised or decentralised manner. The business processes that we specify will coordinate the services that each organisation owns. The second contribution of this thesis is the presentation of a method of describing the observable behaviour of these services. The language we present, SSDL, provides a flexible and extensible way of describing the messaging behaviour of Web Services. We present a method for checking that a set of services described in SSDL are compatible with each other and also that a workflow interacts with a service in the desired manner. The final contribution of this thesis is the presentation of an abstract architecture and prototype implementation of a decentralised workflow engine. The prototype is able to enact workflows described in the Task Model notation in either a centralised or decentralised scenario

UTB/TSC Legacy Degree Programs and Courses 2013 – 2014

https://scholarworks.utrgv.edu/brownsvillelegacycatalogs/1029/thumbnail.jp

Affinity-Based Reinforcement Learning : A New Paradigm for Agent Interpretability

The steady increase in complexity of reinforcement learning (RL) algorithms is accompanied by a corresponding increase in opacity that obfuscates insights into their devised strategies. Methods in explainable artificial intelligence seek to mitigate this opacity by either creating transparent algorithms or extracting explanations post hoc. A third category exists that allows the developer to affect what agents learn: constrained RL has been used in safety-critical applications and prohibits agents from visiting certain states; preference-based RL agents have been used in robotics applications and learn state-action preferences instead of traditional reward functions. We propose a new affinity-based RL paradigm in which agents learn strategies that are partially decoupled from reward functions. Unlike entropy regularisation, we regularise the objective function with a distinct action distribution that represents a desired behaviour; we encourage the agent to act according to a prior while learning to maximise rewards. The result is an inherently interpretable agent that solves problems with an intrinsic affinity for certain actions. We demonstrate the utility of our method in a financial application: we learn continuous time-variant compositions of prototypical policies, each interpretable by its action affinities, that are globally interpretable according to customers’ financial personalities. Our method combines advantages from both constrained RL and preferencebased RL: it retains the reward function but generalises the policy to match a defined behaviour, thus avoiding problems such as reward shaping and hacking. Unlike Boolean task composition, our method is a fuzzy superposition of different prototypical strategies to arrive at a more complex, yet interpretable, strategy.publishedVersio

UTB/TSC Legacy Degree Programs and Courses 2014 – 2015

https://scholarworks.utrgv.edu/brownsvillelegacycatalogs/1030/thumbnail.jp