The Hamlet Application Design Language: introductory definition report

This report provides an introduction to the definition of the Hamlet Application Design Language (ADL). ADL is a graphical-based language and notation supporting the design of parallel real-time applications. Designs expressed in ADL are based on a model of processes that communicate by message-passing. Communication can either be synchronous or asynchronous, and orthogonally, may be subject to blocking, delaying, or nonblocking timing constraints. The language has been devised in such a way that automated (skeletal) code generation can be supported. To this aim, structural aspects are expressed in a notation somewhat similar to data-flow diagrams, whereas behavioral aspects are expressed as state-transition machines following a syntax similar to that of SDL. Exploitation of parallelism is obtained by annotating a design with process replication specifications

Unifying User-to-User Messaging

Unification of user-to-user messaging systems facilitates message exchange independent of time, place, protocol, and end-user device. This article describes an approach to unification that is based on introducing a middleware layer instead of employing gateways. It entails a single system that provides common services such as email, fax, and short messaging, but that can also enable novel services that current messaging systems can't support. The authors also describe how the model can be efficiently implemented on a global scale

Pervasive Messaging

Pervasive messaging is the part of pervasive computing that enables users to communicate with each other. Many of today's electronic messaging systems have their own distinct merits and peculiarities. Pervasive messaging will have to shield the user from these differences. In this paper, we introduce a taxonomy for electronic messaging systems, providing a uniform way to analyze, compare, and discuss electronic messaging systems. With this taxonomy, we analyze the current practice, demonstrating its shortfalls. To overcome these shortfalls, we introduce a novel messaging model: The Unified Messaging System. This system can, in fact, mimic any electronic messaging system, thus providing powerful unified messaging

A comparison of graphical design techniques for parallel, distributed software

We have compared three graphical design techniques, OMT, ADL, and PARSE, on their suitability for the development of parallel/distributed applications. Our method has been to use all three of them in modeling one, existing, application: a backup facility running within the Andrew File System. We compare and analyze the outcomes on a number of important design aspects. Based on this, we draw conclusions on each individual technique and on graphical design techniques for parallel/distributed software in general

Supporting Effective Caching in a Wide-Area Distributed Location Service.

Abstract. Globe is a wide-area distributed system that supports mobile objects. To track and locate objects, we use a worldwide distributed location service, implemented as a search tree. An object registers its current position by storing its address in a nearby leaf node of the tree. This knowledge propagates up to the top of the tree, so every object can be found from the root. Remote objects can cache the location of an object. However, if the object moves, the cache entry is no longer valid. In this paper, we show how caching can be made to work effectively even in the presence of mobile objects. vrije Universitei