Abstract. This paper studies specific language level abstractions for component-based programming. We propose a simple model which captures some basic ingredients — like explicit context dependence, dynamic binding and subtype polymorphism, late (dynamic) composition, and avoidance of inheritance in favor of object composition — that several authors have defended to be central to black-box object-oriented component programming styles. The model is expressed by a core imperative typed calculus, in which components are first-class entities, and whose basic constructs enable the composition, scripting, instantiation and definition of atomic components. Some motivating programming examples are presented, and the operational semantics is shown to enjoy a typesafety property. We also discuss an extension to the Java language aimed at supporting the proposed model, and some implementation issues. 1

In new key-oriented access control systems, access rights are delegated from key to key with chains of signed certificates. This paper describes an efficient graph-search technique for making authorization decisions from certificate databases. The design of the algorithm is based on conceptual analysis of typical delegation network structure and it works well with threshold certificates. Experiments with generated certificate data confirm that it is feasible to find paths of delegation in large certificate sets. The algorithm is an essential step towards efficient implementation of key-oriented access control.

One aspect of multi-agent systems (MAS) that has been only partially studied is their role in software engineering, and in particular their merit as a software architecture style. As we demonstrate, multi-agent systems developed to date have several common architectural characteristics, even though differences in their design and implementation result in variations in their strengths and weaknesses. A large portion of the research in the design and implementation of MAS addresses questions such as: given a computational problem---can one build a MAS to solve it? What should be the properties of this MAS given the problem? Having developed a MAS, what is the class of problems that this MAS, either as developed or with slight modifications, can solve? MAS research has provided several answers to the questions above. However, more fundamental questions were left un-answered: given a computational problem---is a MAS an appropriate solution? If it is, what type of MAS should be preferred? ...

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This paper investigates the use of object-oriented techniques for the specification and design of distributed multimedia applications (DMAs). DMAs are a class of software applications with a range of strong -- often conflicting -- requirements of dynamicity, interactivity, real-time synchronized processing of several media types, network distribution, high-performance, fault-tolerance, load balancing and security. The development of complex DMAs can benefit from the adoption of object design methods and distributed objects implementation technologies. The paper describes the use of two modeling approaches, based on the standard UML modeling language, and on the TRIO formal specification language, respectively. The problem of defining steps to move from the UML or TRIO specification to a CORBA IDL implementation is addressed too. An experimental distributed Video-on-Demand system is used throughout the paper as a case study. 1.

Architectural patterns aid developers in resolving coarse-grained integration problems among components. These patterns are assembled from functionality slices that resolve various communication problems between applications. However, little attention has been paid to how interoperability problems and their resolution are embodied in these patterns. Mapping these problems to specific functionality promises insight into composing integration architectures by illuminating the consistent, high-level solutions that resolve individual conflicts. The objective of this paper is to describe patterns of interoperability conflicts along with their typical resolution in an effort to present reusable solutions for the design of integration architectures. To this end we present the Extender-Controller-Translator (ETC 1) model, and detail its use in a pattern to resolve the problem of data inconsistency.

. In previous work we proposed a simple yet powerful model of components, formally presented by a core calculus, which provides operations for type-safe instantiation and composition of components. In this paper, we discuss the addition of bounded type parameterization to our basic model, and show how it greatly enhances its expressiveness and aplicability. 1 Introduction Component oriented programming (COP) [13] is receiving increasing interest due to the promise of increasing reuse and simplifying software construction. Many component models have appeared [11, 6, 9] but most of their features, remarkably those that concern incremental composition operations lack adequate programming language and static analysis (eg. type-checking) support. In previous work [12], we proposed a simple model of components, formally presented by a core calculus, which provides operations for type-safe instantiation and composition of components. Essential aspects of the core calculus have motivate...

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The term knowledge-based systems, generally refers to expert system approaches to prediction or decision support. In reality, knowledge-based systems include all predictive and decision support models. The growing recognition of the need to integrate, manage, and share knowledge has led to the emergence of the new “magic bullet ” called knowledge management. The “new ” knowledge management paradigm proposes to capture informal knowledge based on personal experience and learning, and to integrate it with more discipline or domain specific formal knowledge in a knowledge base. The current situation The term knowledge management has become popular and we are seeing frequent press references to knowledge management and its importance to the survival of companies in the next millennium. In reality, it is not new. It is, rather, newly popular or perhaps newly understood outside of academic circles. It builds on the successes and failures of data and information management activities and applications. Knowledge management is part of the continuum of data � information � knowledge � wisdom. Knowledge management research is expanding the tools available for knowledge capture beyond