This paper identifies and analyzes the emergence of a new paradigm in software engineering, called separation of concerns, which tries to formally separate the basic algorithm from special purpose concerns such as synchronization, real-time constraints, and location control. This separation allows for the locality of different kinds of information in the programs, making them easier to write, understand, reuse, and modify. We identify the major concerns existing in today's software applications, and analyze recent proposals in the literature that address separation of single concerns. Furthermore, we study the commonalities of these proposals and discuss how they can be used to achieve separation of concerns in general. Finally, we address the problem of composition of several separated concerns.

This paper describes Lua, a language for extending applications. Lua combines procedural features with powerful data description facilities, by using a simple, yet powerful, mechanism of tables. This mechanism implements the concepts of records, arrays, and recursive data types (pointers), and adds some object-oriented facilities, such as methods with dynamic dispatching. Lua presents a mechanism of fallbacks that allows programmers to extend the semantics of the language in some unconventional ways. As a noteworthy example, fallbacks allow the user to add different kinds of inheritance to the language. Currently, Lua is being extensively used in production for several tasks, including user configuration, general-purpose data-entry, description of user interfaces, storage of structured graphical metafiles, and generic attribute configuration for finite element meshes.

this paper is to present a method for handling non-preventable and nonavoidable catastrophic exceptions in embedded hard real-time environments in a well-structured and predictable way, and as painlessly as possible. First, apt hardware and software platforms which are pre-requisite for predictable system behaviour are briefly presented. Then, some existing techniques are shown and their suitability for implementation in embedded hard real-time environments is discussed. Further, a classification of exceptions and our own approach for handling them is presented and elaborated. Finally, a method for the estimation of the resulting temporal behaviour is described. 1 Introduction

Distributed computing has become a complex ecosystem of protocols and services for managing computation and data. Distributed applications are becoming complex as well. Users, particularly in scientific fields, wish to deploy large numbers of applications with complex dependencies and a large appetite for both computation and data. How may such systems and applications be brought together? I propose that applications deployed in distributed systems should be represented by an agent. The role of the agent is to transform an application's abstract operations into concrete operations on the varying resources in a distributed system. The agent must hide the unpleasant aspects of individual resources while coordinating their activity in a manner specialized to each application. I examine four open problems in the design of agents for distributed computing.