Paolo Ciancarini

Agent-Oriented Software Engineering

The ATAL workshops focus on the links between the theory and practice of intelligent agents. One aspect of this, which is steadily growing in importance, is the idea of agent technology as a software engineering paradigm. Previous ATAL workshops have had special tracks on programming languages for agent-oriented development, and methodologies for agent system development. ATAL-99 aims to build on this experience by focussing on the wider issues of agents as a software engineering paradigm.

Coordination models and languages as software integrators

Early concurrent languages supported interactions through shared variables. Languages based on message passing were also a very early idea that gained popularity as soon as software engineers started to design and build software for distributed computer systems. A more recent approach consists of using higher-level programming models and languages for distributed programming, called coordination models and languages. “A coordination model is the glue that binds separate activities into an ensemble” [Carriero and Gelernter 1992]. In other words, a coordination model provides a framework in which the interaction of active and independent entities called agents can be expressed. A coordination model should cover the issues of creation and destruction of agents, communication among agents, and spatial distribution of agents, as well as synchronization and distribution of their actions over time. A constructive approach to define coordination models consists of identifying the components out of which they are built:

Agent-Oriented Software Engineering II

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Coordination Languages and Models

Invited Papers.- Coordination and Access Control of Mobile Agents.- Characteristics of an Agent Scripting Language and its Execution Environment.- Regular Papers.- A Coordination Model for Agents based on Secure Spaces.- Coordination with Attributes.- MobiS: A Specification Language for Mobile Systems.- Coordinated Roles: Promoting Re-usability of Coordinated Active Objects Using Event Notification Protocols.- Pipelining the Molecule Soup: A Plumbers Approach to Gamma.- Erratic Fudgets: A Semantic Theory for an Embedded Coordination Language.- Coordination of Synchronous Programs.- Composing Specications for Coordination.- On the Expressiveness of Coordination Models.- Comparing Software Architectures for Coordination Languages.- A Hierarchical Model for Coordination of Concurrent Activities.- A Self-Deploying Election Service for Active Networks.- Mobile Co-ordination: Providing Fault Tolerance in Tuple Space Based Co-ordination Languages.- A Simple Extension of Java Language for Controllable Transparent Migration and its Portable Implementation.- Coordination Among Mobile Objects.- Simulation of Conference Management using an Event-Driven Coordination Language.- Internet-Based Coordination Environments and Document-Based Applications: a Case Study.- Coordination of a Parallel Proposition Solver.- CLAM: Composition Language for Autonomous Megamodules.- Modeling Resources for Activity Coordination and Scheduling.- Static Analysis of Real-Time Component-based Systems Congurations.- Acme-based Software Architecture Interchange.- A Group Based Approach for Coordinating Active Objects.- Introducing Connections Into Classes With Static Meta-Programming.- TRUCE: Agent Coordination Through Concurrent Interpretation of Role-Based Protocols.- The STL++ Coordination Language: A Base for Implementing Distributed Multi-agent Applications.- Posters.- A Distributed Semantics for a IWIM-Based Coordination Language.- Coordination in Context: Authentication, Authorisation and Topology in Mobile Agent Applications.- Presence and Instant Messaging via HTTP/1.1: A Coordination Perspective.- Towards a Periodic Table of Connectors.

The concurrent language, Shared Prolog

Shared Prolog is a new concurrent logic language. A Shared Prolog system is composed of a set of parallel agents that are Prolog programs extended by a guard mechanism. The programmer controls the granularity of parallelism, coordinating communication and synchronization of the agents via a centralized data structure. The communication mechanism is inherited from the blackboard model of problem solving. Intuitively, the granularity of the logic processes to be elaborated in parallel is large, while the resources shared on the blackboard can be very fined grained. An operational semantics for Shared Prolog is given in terms of a distributed model. Through an abstract notion of computation, the kinds of parallelism supported by the language, as well as properties of infinite computations, such as local deadlocks, are studied. The expressiveness of the language is shown with respect to the specification of two classes of applications: metaprogramming and blackboard systems.

Coordinating multiagent applications on the WWW: a reference architecture

The original Web did not support multiuser, interactive applications. This shortcoming is being studied, and several approaches have been proposed to use the Web as a platform for programming Internet applications. However, most existing approaches are oriented to centralized applications at servers, or local programs within clients. To overcome this deficit, we introduce PageSpace, that is a reference architecture for designing interactive multiagent applications. We describe how we control agents in PageSpace, using variants of the coordination language Linda to guide their interactions. Coordination technology is integrated with the standard Web technology and the programming language Java. Several kinds of agents live in the PageSpace: user interface agents, personal homeagents, agents that implement applications, and agents which interoperate with legacy systems. Within our architecture, it is possible to support fault-tolerance and mobile agents as well.

Architecting families of software systems with process algebras

Software components can give rise to several kinds of architectural mismatches when assembled together in order to form a software system. A formal description of the architecture of the resulting component-based software system may help to detect such architectural mismatches and to single out the components that cause the mismatches. In this article, we concentrate on deadlock-related architectural mismatches arising from three different causes that we identify: incompatibility between two components due to a single interaction, incompatibility between two components due to the combination of several interactions, and lack of interoperability among a set of components forming a cyclic topology. We develop a process algebra-based architectural description language called PADL, which deals with all three causes through an architectural compatibility check and an architectural interoperability check relying on standard observational equivalences. The adequacy of the architectural compatibility check is assessed on a compressing proxy system, while the adequacy of the architectural interoperability check is assessed on a cruise control system. We then address the issue of scaling the architectural compatibility and interoperability checks to architectural styles through an extension of PADL. The formalization of an architectural style is complicated by the presence of two degrees of freedom within the set of instances of the style: variability of the internal behavior of the components and variability of the topology formed by the components. As a first step towards the solution of the problem, we propose an intermediate abstraction called architectural type, whose instances differ only for the internal behavior of their components. We define an efficient architectural conformity check based on a standard observational equivalence to verify whether an architecture is an instance of an architectural type. We show that all the architectures conforming to the same architectural type possess the same compatibility and interoperability properties.

Managing complex documents over the WWW: a case study for XML

The use of the World Wide Web as a communication medium for knowledge engineers and software designers is limited by the lack of tools for writing, sharing, and verifying documents written with design notations. For instance, the Z language has a rich set of mathematical characters, and requires graphic-rich boxes and schemas for structuring a specification document. It is difficult to integrate Z specifications and text on WWW pages written with HTML, and traditional tools are not suited for the task. On the other hand, a newly proposed standard for markup languages, namely XML, allows one to define any set of markup elements; hence, it is suitable for describing any kind of notation. Unfortunately, the proposed standard for rendering XML documents, namely XSL, provides for text-only (although sophisticated) rendering of XML documents, and thus it cannot be used for more complex notations. We present a Java-based tool for applying any notation to elements of XML documents. These XML documents can thus be shown on current-generation WWW browsers with Java capabilities. A complete package for displaying Z specifications has been implemented and integrated with standard text parts. Being a complete rendering engine, text parts and Z specifications can be freely intermixed, and all the standard features of XML (including HTML links and form elements) are available outside and inside Z specifications. Furthermore, the extensibility of our engine allows any additional notations to be supported and integrated with the ones we describe.

Jada - Coordination and Communication for Java Agents

In this chapter we are going to analyze mobile code issues in the perspective of object oriented systems in which thread migration is not supported. This means that both objects code and data can be transmitted from a place to another but not the current execution state (if any) associated to the object. This is the case with the Java language which is often used in the Word Wide Web for developing applets which are little applications downloaded on the fly and executed in the client machine. While this mechanism is quite useful for enhancing HTML documents with sound and animation, we think that this technology can give its best in the field of distributed-cooperative work, both in the perspective of Internet and Intranet connectivity. Java is indeed a concurrent, multithreaded language, but it offers little help for distributed programming. Thus, we introduce Jada, a coordination toolkit for Java where coordination among either concurrent threads or distributed Java objects is achieved via shared object spaces. By exchanging objects through tuple spaces, Java programs and applets can exchange data or synchronize their actions over a single host, a LAN, or even the Internet.

PageSpace: an architecture to coordinate distributed applications on the Web

Abstract Most applications on the Web require active processing and coordination of services and components. Today, activity within the Web is tied to server machines and there is no integrated mechanism that allows it to coordinate activity located at clients, such as applets. In order to allow for really distributed application in the Web, such coordination platforms have to be built. The PageSpace is a platform to support open distributed application on top of the Web. It utilizes Java to execute distributed agents that coordinate their exchange of services by Linda-like coordination technology. The PageSpace architecture comprises a set of agent classes. The user-interfaces is manifested are Alpha agents displayed in Web browsers. The representation of the user on the net is its homeagent, called Beta, which uses services on behalf of the user. Applications are formed by Delta agents that offer and use services. The coordination amongst agent is performed using a shared space of information and Linda-like primitives that operate on it. With the PageSpace architecture, distributed applications on top of the Web and the Internet are enabled, as the platform decentralizes activity. By combining coordination technology with the Web and Java, the centralized, server-bound structure of todays Web-applications is replaced with a truly open distributed system.