Emilio Tuosto

The Klaim Project: Theory and Practice

Klaim (Kernel Language for Agents Interaction and nMobility) is an experimental language specifically designed to nprogram distributed systems consisting of several mobile ncomponents that interact through multiple distributed tuple nspaces. Klaim primitives allow programmers to distribute and nretrieve data and processes to and from the nodes of a net. nMoreover, localities are first-class citizens that can be ndynamically created and communicated over the network. Components, nboth stationary and mobile, can explicitly refer and control the nspatial structures of the network. n nThis paper reports the experiences in the design and development nof Klaim. Its main purpose is to outline the theoretical nfoundations of the main features of Klaim and its programming nmodel. We also present a modal logic that permits reasoning about nbehavioural properties of systems and various type systems that nhelp in controlling agents movements and actions. Extensions of nthe language in the direction of object oriented programming are nalso discussed together with the description of the implementation nefforts which have lead to the current prototypes.

A LTS Semantics of Ambients via Graph Synchronization with Mobility

We present a simple labelled transition system semantics of Cardelli and Gordons Ambient calculus. We exploit a general and flexible model based on (hyper)graphs, where graph transformation is obtained via (hyper)edge replacement and local synchronization with mobility. In addition to tree-like ambients, the calculus we define works just as well with graph-like ambients, which are a more realistic model of internetworks.

A process calculus for qos-aware applications

The definition of suitable abstractions and models for identifying, understanding and managing Quality of Service (QoS) constraints is a challenging issue of the Service Oriented Computing paradigm. In this paper we introduce a process calculus where QoS attributes are first class objects. We identify a minimal set of primitives that allow capturing in an abstract way the ability to control and coordinate services in presence of QoS constraints.

A Formal Basis for Reasoning on Programmable QoS

The explicit management of Quality of Service (QoS) of network connectivity, such as, e. g., working cost, transaction support, and security, is a key requirement for the development of the novel wide area network applications. In this paper, we introduce a foundational model for specification of QoS attributes at application level. The model handles QoS attributes as semantic constraints within a graphical calculus for mobility. In our approach QoS attributes are related to the programming abstractions and are exploited to select, configure and dynamically modify the underlying system oriented QoS mechanisms.

From theory to practice in transactional composition of web services

We address the problem of composing Web Services in long-running transactional business processes, where compensations must be dealt with appropriately. The framework presented in this paper is a Java API called Java Transactional Web Services (jtws), which provides suitable primitives for wrapping and invoking Web Services as activities in long-running transactions. jtws adheres to a process calculi formalisation of long-running transactions, called saga, which fixes unambiguously the implemented compensation policy. In particular, the primitives provided by jtws are in one-to-one correspondence with the primitives of sagas,and they are abstract enough to hide the complex details of their realization, thus favouring usability. Moreover, jtws orchestrates business processes in a distributed way.

Coalgebraic minimization of HD-automata for the π-calculus using polymorphic types

We introduce finite-state verification techniques for the π-calculus whose design and correctness are justified coalgebraically. In particular, we formally specify and implement a minimization algorithm for HD-automata derived from π-calculus agents. The algorithm is a generalization of the partition refinement algorithm for classical automata and is specified as a coalgebraic construction defined using λ→, Φ, Σ, a polymorphic λ-calculus with dependent types. The convergence of the algorithm is proved; moreover, the correspondence of the specification and the implementation is shown.

Synchronized hyperedge replacement for heterogeneous systems

We present a framework for modelling heterogeneous distributed systems using graph transformations in the Synchronized Hyperedge Replacement approach, which describes complex evolutions by synchronizing local rules. In order to deal with heterogeneity, we consider different synchronization algebras for different communication channels. The main technical point is the interaction between synchronization algebras and name mobility in the π-calculus style. The power of our approach is shown through a few examples.

Model checking for nominal calculi

Nominal calculi have been shown very effective to formally model a variety of computational phenomena. The models of nominal calculi have often infinite states, thus making model checking a difficult task. In this note we survey some of the approaches for model checking nominal calculi. Then, we focus on History-Dependent automata, a syntax-free automaton-based model of mobility. History-Dependent automata have provided the formal basis to design and implement some existing verification toolkits. We then introduce a novel syntax-free setting to model the symbolic semantics of a nominal calculus. Our approach relies on the notions of reactive systems and observed borrowed contexts introduced by Leifer and Milner, and further developed by Sassone, Lack and Sobocinski. We argue that the symbolic semantics model based on borrowed contexts can be conveniently applied to web service discovery and binding.

A Coordination-based Methodology for Security Protocol Verification

The quest for the formal certification of properties of systems is one of the most challenging research issues in the field of formal methods. It requires the development of formal models together with effective verification techniques. In this paper, we describe a formal methodology for verifying security protocols based on ideas borrowed from the analysis of open systems, where applications interact with one another by dynamically sharing common resources and services in a not fully trusted environment. The methodology is supported by ASPASyA, a tool based on symbolic model checking techniques.

Graph-Based Models of Internetworking Systems

Graphical notations have been widely accepted as an expressive and intuitive working tool for system specification and design. This paper outlines a declarative approach based on (hyper-)graphs and graph synchronization to deal with the modeling of Wide Area Network applications. This paper aims at contributing to the understanding of crucial issues involved in the specification and design of Wide Area Network systems, as a first step toward the development of software engineering techniques and tools for designing and certificating internetworking systems.