... this article, we analyze several quorum types in order to better understand their behavior in practice. The results obtained challenge many of the assumptions behind quorum based replication. Our evaluation indicates that the conventional read-one/write-all-available approach is the best choice for a large range of applications requiring data replication. We believe this is an important result for anybody developing code for computing clusters as the read-one/write-all-available strategy is much simpler to implement and more flexible than quorum-based approaches. In this article, we show that, in addition, it is also the best choice using a number of other selection criteria

The increasingly widespread use of cluster architectures has resulted in many new application scenarios for data replication. While data replication is, in principle, a well understood problem, recovery of replicated systems has not yet received enough attention. In the case of clusters, recovery procedures are particularly important since they have to keep a high level of availability even during recovery. In fact, recovery is part of the normal operations of any cluster as the cluster is expected to continue working while sites leave or join the system. The question is then how to optimize recovery so that it can be done without redundancies (that would affect the performance) and with minimal disruptions to normal operations. In this paper, we identify different performance and availability problems that are caused by recovery and propose an online recovery protocol to overcome them.

The CoSy Architecture Schema Toolkit (CAST) is a new software toolkit, and related processing paradigm, which supports the construction and exploration of information-processing architectures for intelligent systems such as robots. CAST eschews the standard point-to-point connectivity of traditional message-based software toolkits for robots, instead supporting the parallel refinement of representations on shared working memories. In this article we focus on the engineering-related aspects of CAST, including the challenges that had to be overcome in its creation, and how it allow us to design and build novel intelligent systems in flexible ways. We support our arguments with example drawn from recent engineering efforts dedicated to building two intelligent systems with similar architectures: the PlayMate system for tabletop manipulation and the Explorer system for human-augmented mapping. Key words: intelligent robotics, artificial intelligence, information-processing architectures, middleware 1.

The last decade has seen the emergence and popularisation of middleware technologies, such as the OMG’s Common Object Request Broker Architecture (CORBA), Microsoft’s Distributed Component Object Model (DCOM) and Sun’s Java RMI. These technologies have profoundly changed the way distributed applications are developed. In particular, they enable the large-scale deployment of applications in distributed heterogeneous environments, by making transparent the distribution aspects and enabling the developers to focus on application concerns. Importantly, the dissemination of distributed systems technology has also stimulated the emergence of new application areas, such as distributed multimedia and mobile applications. However, due to the dynamic nature of these new applications, current middleware technologies have proven inadequate. The major reason for this is the currently dominating “black-box ” philosophy for middleware design, which precludes the flexible configuration and adaptation of a platform in order to suit the particular and evolving requirements of different applications. This thesis

Efficiency oriented activities require some people to collaborate in order to achieve better results. People, who don't necessarily know to each other, need to be organized, communicated, and coordinated effectively to achieve a successful outcome. Today's technological advances permit to set up a group of handheld and wireless devices as a network infrastructure for the development of applications to satisfy the mentioned needs. We have designed a agent-based middleware to develop applications that consider not only knowledge and skills of the participants but also physical distance and psycho-social characteristics. In order to explain how to support spontaneous collaboration among people different situations, we describe how to build some kind of applications using the developed middleware. We expect to obtain a tool which not only can provide an adequate communication medium or enhance productivity in developing applications, but also becomes a facilitator of collaboration.

Client-side firewall and/or proxy

Distributed User Interfaces (DUIs) are those interfaces whose different parts can be distributed in time and space on different monitors, screens, and computing platforms, depending on several parameters expressing the context of use, such as the user, the computing platform, and the physical environment in which the user is carrying out her interactive task. To understand and classify existing approaches for DUIs and to identify underexplored situations of DUIs, a reference model for DUIs is introduced that examines DUIs according to four ‘C ’ dimensions: computation (what is distributed?), communication (when is it distributed?), coordination (who is it distributed?), and configuration (from where and to where is the distribution operated?). At the core of this reference model exists the original notion of user interface habitat, that is the place where a particular type of user interface is normally found. According to this notion, it is possible to explore and investigate a wide spectrum of DUIs among which we exemplify several cases coming from our existing research and development of DUIs. 1.