Abstract. Broadcast protocols are a fundamental building block for implementing replication in fault-tolerant distributed systems. This paper addresses secure service replication in an asynchronous environment with a static set of servers, where a malicious adversary may corrupt up to a threshold of servers and controls the network. We develop a formal model using concepts from modern cryptography, give modular definitions for several broadcast problems, including reliable, atomic, and secure causal broadcast, and present protocols implementing them. Reliable broadcast is a basic primitive, also known as the Byzantine generals problem, providing agreement on a delivered message. Atomic broadcast imposes additionally a total order on all delivered messages. We present a randomized atomic broadcast protocol based on a new, efficient multi-valued asynchronous Byzantine agreement primitive with an external validity condition. Apparently, no such efficient asynchronous atomic broadcast protocol maintaining liveness and safety in the Byzantine model has appeared previously in the literature. Secure causal broadcast extends atomic broadcast by encryption to guarantee a causal order among the delivered messages. Our protocols use threshold cryptography for signatures, encryption, and coin-tossing.

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The early stages of building design involve the consideration of different design variants and their assessment regarding various performance criteria including energy consumption and costs. During the design process, the involved experts from different disciplines frequently exchange building information to develop a design that satisfies the project’s requirements and objectives. In the course of this iterative process, the building design evolves throughout multiple refinement stages. At the same time, different variants are developed. In BIM-based projects, the maturity of the design information provided by the model is expressed by the notion of Level of development (LOD). So far, however, there is no method to formally define the information requirements of a LOD. In particular, there are no means for expressing the uncertainty involved with the provided information. By contrast, despite the insufficient information available in early design stages, a BIM model appears precise and certain. This situation leads to false assumptions and model evaluations, for example, in the case of energy efficiency calculations or structural analysis. Hence, this paper presents an overview of a set of approaches that were developed to alleviate and preserve the consistency of the designed solutions. The approach includes the development of a multi-LOD meta-model, which allows one to explicitly describe the LOD requirements of each building component type incorporating the possible uncertainties, e.g. concerning the building dimensions. On the basis of this multi-LOD model, methods for evaluating a building design’s performance regarding the building’s structure and life cycle energy performance are proposed that take the defined uncertainties into account. To support the management of design variants in one consistent model, a graph-based approach is introduced. Finally, a minimized communication protocol is described to facilitate the workflow and communicate the evaluation results for supporting the decision-making process.

Abstract. The consequences of architectural planning and design decisions made in the early design phases are hard to foresee. While professionals are used to reading plans and understanding architectural models, most laypeople are not familiar with their abstractions. This can lead to misinterpretations and misunderstandings between the different participants in the design process, especially in complex building situations, and decisions can be made or rejected that can have far-reaching consequences for the remainder of the project.In this paper we describe the concept and prototypical implementation of a decision-support system for the early design and discussion stages of urban design projects that aims to address precisely this problem. The setup directly connects physical volumetric models and hand-drawn sketches with an interactive, mixedreality visualization presented on a tablet or mobile phone, making it possible to see an interactive real-time view of an architectural design within the context of the actual site. In addition, the system is able to incorporate interactive simulations conducted on the model and presented in the AR-view. Keywords: Early design stages · Urban design · HCI · Tangible interfaces · Immersive environment · Simulations ProblemDuring the early design phases presentations and discussions between architects and clients usually involve sketches, paper and models. While designers are used to working intuitively with these tools, laypeople are not used to reading plans or scale models and find it difficult to relate these abstract representations to the real world. Many people, therefore, find it hard to assess the impact of design decisions at this stage for the later result.An alternative means of presentation is the use of perspective drawings and visualisations that show how an architectural design will look in a real scenario or the actual context. With the availability of affordable and ever more powerful computers, handdrawn perspectives have mostly been replaced by digital visualisations, initially in the form of individual rendered images and more recently in the form of immersive and © Springer-Verlag Berlin Heidelberg 2015 G.