The Planning Spectrum - One, Two, Three, Infinity

Linear Temporal Logic (LTL) is widely used for defining conditions on the execution paths of dynamic systems. In the case of dynamic systems that allow for nondeterministic evolutions, one has to specify, along with an LTL formula f, which are the paths that are required to satisfy the formula. Two extreme cases are the universal interpretation A.f, which requires that the formula be satisfied for all execution paths, and the existential interpretation E.f, which requires that the formula be satisfied for some execution path. When LTL is applied to the definition of goals in planning problems on nondeterministic domains, these two extreme cases are too restrictive. It is often impossible to develop plans that achieve the goal in all the nondeterministic evolutions of a system, and it is too weak to require that the goal is satisfied by some execution. In this paper we explore alternative interpretations of an LTL formula that are between these extreme cases. We define a new language that permits an arbitrary combination of the A and E quantifiers, thus allowing, for instance, to require that each finite execution can be extended to an execution satisfying an LTL formula (AE.f), or that there is some finite execution whose extensions all satisfy an LTL formula (EA.f). We show that only eight of these combinations of path quantifiers are relevant, corresponding to an alternation of the quantifiers of length one (A and E), two (AE and EA), three (AEA and EAE), and infinity ((AE)* and (EA)*). We also present a planning algorithm for the new language that is based on an automata-theoretic approach, and study its complexity

АВТОМАТИЗОВАНА КОМПОЗИЦІЯ СЕМАНТИЧНИХ ВЕБ-СЕРВІСІВ У ВИКОНУВАНІ ПРОЦЕСИ. ПЕРЕКЛАД СТАТТІ «AUTOMATED COMPOSITION OF SEMANTIC WEB SERVICES INTO EXECUTABLE PROCESSES\ud (ПЕРЕКЛАД РЕМАРОВИЧ С.)\ud

Пропонується метод планування для автоматизованої композиції Веб-сервісів, які описані в OWL-S моделях процесу, який може\ud ефективно боротися з недетермінізмом, частковою спостережністю і складними цілями.\ud \ud Abstract\ud Different planning techniques have been applied to the problem of automated composition of web services. However, in realistic cases, this planning problem is far from trivial: the planner needs to deal with the nondeterministic behavior of web services, the partial observability of their internal status, and with complex goals expressing temporal conditions and preference requirements. We propose a planning technique for the automated composition of web services described in OWL-S process models, which can deal effectively with nondeterminism, partial observability, and complex goals. The technique allows for the synthesis of plans that encode compositions of web services with the usual programming constructs, like conditionals and iterations. The generated plans can thus be translated into executable processes, e.g., BPEL4WS programs. We implement our solution in a planner and do some preliminary experimental evaluations that show the potentialities of our approach, and the gain in performance of automating the composition at the semantic level w.r.t. the automated composition at the level of executable processes

Fresh-Register Automata

What is a basic automata-theoretic model of computation with names and fresh-name generation? We introduce Fresh-Register Automata (FRA), a new class of automata which operate on an infinite alphabet of names and use a finite number of registers to store fresh names, and to compare incoming names with previously stored ones. These finite machines extend Kaminski and Francez’s Finite-Memory Automata by being able to recognise globally fresh inputs, that is, names fresh in the whole current run. We exam-ine the expressivity of FRA’s both from the aspect of accepted languages and of bisimulation equivalence. We establish primary properties and connections between automata of this kind, and an-swer key decidability questions. As a demonstrating example, we express the theory of the pi-calculus in FRA’s and characterise bisimulation equivalence by an appropriate, and decidable in the finitary case, notion in these automata

Automated synthesis of executable web service compositions from BPEL4WS processes

We propose a technique for the automated synthesis of new com-posite web services. Given a set of abstract BPEL4WS descriptions of component services, and a composition requirement, we auto-matically generate a concrete BPEL4WS process that, when exe-cuted, interacts with the components and satisfies the requirement. We implement the proposed approach exploiting efficient repre-sentation techniques, and we show its scalability over case stud-ies taken from a real world application and over a parameterized domain

АВТОМАТИЗОВАНИЙ СИНТЕЗ КОМПОЗИТНИХ BPEL4WS ВЕБ-СЕРВІСІВ. ПЕРЕКЛАД СТАТТІ «AUTOMATED SYNTHESIS OF COMPOSITE BPEL4WS WEB SERVICES» (ПЕРЕКЛАД РЕМАРОВИЧ С.)

У цій статті ми пропонуємо метод для автоматизованого синтезу нових композитних Веб-сервісів. Враховуючи набір абстрактних BPEL4WS описів компонентних сервісів, а також вимогу композиції, ми автоматично генеруємо виконуваний BPEL4WS процес, який, після розгортання, здатний взаємодіяти з компонентами, щоб задовольнити вимогу. Ми реалізували запропонований підхід, використовуючи ефективні засоби синтезу, і експеримент з деякими тематичними дослідженнями, взятими з реальних застосувань і з параметризованим доменом. Ми показали, що метод може масштабуватися до випадків, в яких ручна розробка BPEL4WS композитних сервісів не є тривіальною і вимагає багато часу

ПІДХІД ДЛЯ АВТОМАТИЗОВАНОЇ КОМПОЗИЦІЇ BPEL ПРОЦЕСІВ / ПЕРЕКЛАД СТАТТІ «AN APPROACH FOR THE AUTOMATED COMPOSITION OF BPEL PROCESSES» (ПЕРЕКЛАД РЕМАРОВИЧ С.)

Ми описуємо метод для автоматизованого синтезу нових композитних Веб-сервісів. Враховуючи набір компонентних сервісів, які описані як абстрактні BPEL4WS процеси, збагачені семантичними анотаціями, а також враховуючи вимогу композиції, ми автоматично генеруємо виконуваний BPEL4WS процес, який після розгортання здатний взаємодіяти з компонентами, щоб задовольнити вимогу. Ми орієнтуємося, зокрема, на опис анотацій, які ми повинні додати до \ud абстрактних BPEL4WS процесів для того, щоб охопити «семантичні» аспекти їх виконання, і на роль, яку ці семантичні анотації грають в завданні автоматизованої композиції

Automated synthesis of composite BPEL4WS Web services

In this paper we propose a technique for the automated synthesis of new composite web services. Given a set of ab-stract BPEL4WS descriptions of component services, and a composition requirement, we automatically generate an ex-ecutable BPEL4WS process that, once deployed, is able to interact with the components to satisfy the requirement. We implement the proposed approach exploiting efficient syn-thesis techniques, and experiment with some case studies taken from real world applications and with a parameter-ized domain. We show that the technique can scale up to cases in which the manual development of BPEL4WS com-posite services is not trivial and is time consuming.

Control flow requirements for automated service composition

n/

Service composition in stochastic settings

With the growth of the Internet-of-Things and online Web services, more services with more capabilities are available to us. The ability to generate new, more useful services from existing ones has been the focus of much research for over a decade. The goal is, given a specification of the behavior of the target service, to build a controller, known as an orchestrator, that uses existing services to satisfy the requirements of the target service. The model of services and requirements used in most work is that of a finite state machine. This implies that the specification can either be satisfied or not, with no middle ground. This is a major drawback, since often an exact solution cannot be obtained. In this paper we study a simple stochastic model for service composition: we annotate the tar- get service with probabilities describing the likelihood of requesting each action in a state, and rewards for being able to execute actions. We show how to solve the resulting problem by solving a certain Markov Decision Process (MDP) derived from the service and requirement specifications. The solution to this MDP induces an orchestrator that coincides with the exact solution if a composition exists. Otherwise it provides an approximate solution that maximizes the expected sum of values of user requests that can be serviced. The model studied although simple shades light on composition in stochastic settings and indeed we discuss several possible extensions