We introduce a new declarative language called SELECTSCRIPT. As its name suggests, it is a scripting language inspired primarily by SQL and its relational algebra. It is intended to be used for complex queries on different kinds of world models. Scripts can be dynamically generated and executed, or embedded into the code of foreign programming languages. A first interpreter was therefore developed for Python. Adapting the ideas of language-oriented programming, which enables developers to create their own domain-specific language, we developed a language stub that can be easily adapted and extended to comply with any (discrete) robotic world model or robotic simulator. We will further show how simple SELECT-statements can be used to extract any kind of valuable information in various return formats, thereby going beyond traditional SQL capabilities.

The traditional, isolated data handling in sensor-actuator systems does not fulfill the requirements of robots that need to interact with their smart environment. Consequently, we have to develop new mechanisms for adaptive data and context handling. We firstly investigate what types of data are present within smart environments and how they can be classified and organized. Only if the available data can be structured, it can be queried and thus put into context. This is important because the variety of data and possible interpretations is tremendous, ranging from measurement values, sensor and robot descriptions/states/commands, to environmental data, such as positions, maps, spatial relations, etc. To cope with this diversity, we developed a solution capable of storing and accessing data within a distributed environment by providing additional context information. Furthermore, we describe how this information can be assembled in a task-oriented manner. This enables robots to dynamically generate environmental abstractions by using data from different sources and also enables them to incorporate external sensor measurements.

Distributed applications dealing with data from networked sensors need some indication about the quality of remote information. This paper describes how to derive a dynamic validity value that represents a measure for the confidence in remote sensor data. In contrast to conventional systems which treats a typical processing chain as a whole, this paper describes how individual characteristic of sensing, detection and filter mechanisms can be assessed and how this assessment can be evaluated to a single validity value. In particular the paper defines respective operations combining the run-time validity estimates of every stage in a processing chain. The combination is evaluated by rules as part of a failure algebra. The paper presents the generation of an application specific validity value which is finally demonstrated in a robotic application.

A plethora of (secure) routing protocols exists for wireless multihop networks. These protocols are mostly tailored to meet the performance and security requirements of specific application scenarios. As a result, the protocols cannot easily be adapted to novel application demands, organically growing networks, etc. We argue that the modular design of routing protocols and security mechanisms can remove the key limitations of today's monolithic routing protocols. We show the feasibility of a modular routing approach for wireless multihop networks using the example of a wireless mesh network. In particular, we demonstrate that a dynamic switch between protocol modules is possible at runtime by means of simulation as well as testbed experimentation. We further demonstrate that the security associations and the key material can be reutilized for bootstrapping novel protocol modules, thus minimizing the control overhead.

Achieving RF connectivity is a critical issue in any wireless application. This is particularly challenging in mobile applications, as links are up and down many times. In such scenarios, where nodes keep on moving, it would be interesting for them to have knowledge of their remaining RF connectivity time. Such information can be used, for instance, to improve existing network protocols. The current paper addresses this problem by presenting the so-called Oriented Birth-Death (O-BD). The proposed solution is a modified version of the existing Birth-Death (BD) prediction model. We introduce in this work the notion of orientation to represent a tendency in the link future state. In other words, it considers if the link tends to increase or decrease the signal strength to make the prediction. Thereby a considerable prediction improvement is obtained, as shown in the evaluation performed. The proposed solution is well suited for mobile wireless sensor networks, whose nodes have low computational power and should be energy harvesting.

Developing complex sensor/actuator systems, like robot applications, is challenged by a multitude of different hardware platforms, networks, programming languages, data formats, etc. In this paper, we present our architecture that copes with this heterogeneity and allows for a flexible composition of smart sensors and actuators. The main focus lies on a two layered approach combining the communication middleware FAMOUSO and the programming abstraction MOSAIC. FAMOUSO enables the information exchange between networked systems, hides the high degree of heterogeneity on hardware and network level, and is usable from different programming environments. MOSAIC uses FAMOUSO and provides a generic access to the exchanged information. Furthermore, it offers a way to abstract from different sensor and actuator hardware and provides a framework for application development with predefined components, enabling comprehensive fault detection. The paper concludes with a case study that shows how the middleware and programming abstractions are used to build a distributed modular system for a robot manipulator.

Hospitals aim at an extensive continuous monitoring of patients. This enables the personal to check the conditions of a patient anywhere at any given time and allows them to immediately react to anomalies and emergencies. The same technology can be used to instantaneously visualize available patient data using augmented reality techniques.

Autonomous, active components like smart sensors and actuators offer the capabilities of spontaneous behaviour, concurrent computations and well-defined communication interfaces. The perspective of building a system from such active blocks however has an impact on modeling and deployment of the components and supporting their interaction at run-time. The paper presents a modeling approach for dynamically interacting autonomous objects addressing the problems of independent development, deployment and incremental extension. Compared to related approaches our concept further complements the modeling by an adequate middleware that supports the abstractions of the model during run-time and performs the respective dynamic binding and co-operation between objects. This opens a wide range of possibilities for dynamically integrating hardware and software components and support virtual sensors and actuators.

This paper addresses questions of using wireless mesh networks (WMNs) in heterogeneous industrial infrastructures. This implies several problems like global addressing, handling of QoS requirements, interconnection with embedded networks. Our proposed solution is a publish/subscribe middleware. We discuss how it solves the mentioned problems. Real-world measurements and simulation results give an idea of QoS properties. A case study of controlling a mobile robot is presented. The results show that the middleware is well suited for non-critical control and monitoring tasks.

This paper describes an approach on the way towards dynamically configuring an application by discovering and using smart devices in a sensor/actuator network. The key to this are self-describing smart devices. Self description means that all information necessary to use the respective device are stored within the device itself. As an appropriate description language XML has emerged during the last years. XML provides considerable flexibility and ease of post-processing using XSLT stylesheets. However, because of stringent space constraints, there is the need to have a more compact representation. We describe what information is stored, what it can be used for, and how we make this information accessible during run-time

Distributed factory automation systems benefit from field-busses which, in general, provide support for reliable and timely communication. These field-buses, however, provide rather low level communication objects and their features regarding quality aspects of communication are difficult to access and use for applications. The paper presents COSMIC (cooperating smart devices), a middleware architecture which allows the use of communication abstraction for high level applications based on distributed cooperating objects. The middleware supports an event-based communication model which enables spontaneous dissemination of events, maintains control autonomy of objects and allows to specify different real-time and reliability requirements on the application level. The basic abstractions presented at the middleware layer are events and event channels. As an example, the paper describes how these abstractions are mapped to CAN-Bus which constitutes a widely used field-bus standard.

This paper compares interaction and communication mechanisms used in distributed control systems, focusing on object-oriented and component-based development. The standard communication model used in distributed object oriented systems is remote method invocation. We argue that this client/server oriented model has some severe drawbacks when used in a control system where objects may have to broadcast information, spontaneously communicate environmental changes and where control autonomy is a crucial requirement. Therefore, we compare the traditional way of object invocation with a port-based scheme and the model of event channels. An application scenario from robot control is used to highlight similarities and differences among these mechanisms.

Designing distributed real-time systems as being composed of communicating objects offers many advantages with respect to modularity and extensibility of these systems. However, distributed real-time applications exhibit communication patterns that significantly differ from the traditional object invocation style. The publisher/subscriber model for inter-object communication matches well with these patterns. Any implementation of that model must address the problems of binding subscribers to publishers, of routing and filtering of messages, as well as reliability, efficiency and latency of message delivery. In the context of real-time applications, all these issues must be subject to a rigid inspection with respect to meeting real-time requirements. We argue that for embedded control systems built around smart microcontroller-powered devices these requirements can only be met when exploiting the properties of the underlying network. The CAN-Bus (CAN: Controller Area Network) which is an emerging standard in the field of real-time embedded systems is particularly suited to implement a publisher/subscriber model of communication. We present an implementation of the real-time publisher/subscriber model that exploits the underlying facilities of the CAN-Bus. In particular, we introduce a novel addressing scheme for publisher/subscriber communication that makes efficient use of the CAN-Bus addressing method. We provide a detailed design and implementation details along with some preliminary performance estimations.

The paper focuses on method invocation of real-time objects in a CAN-based distributed real-time system. A simple object model is introduced, which allows the convenient modelling of hardware and software components. Related to the object model, two issues are discussed. Firstly, a model is introduced which allows to form and address object groups. This reflects a basic need in a real-time system to distribute information to multiple clients efficiently. Secondly, the paper discusses an approach to express timing requirements for object invocations. To achieve distributed consensus on communication resource access, an EDF-like approach is introduced, which takes advantage of knowledge about deadlines, the number of remaining communication activities and the remaining worst-case execution time for the invoked method at each point of time.

A novel and efficient group communication (multicast) protocol, based on a single logical-clock token ring approach, is described. The protocol is highly efficient and it guarantees total ordering and atomicity of multicast messages for asynchronous distributed systems. Unlike other logical token-ring algorithms, the protocol does not have a problem of token loss. The optimized fault-tolerant algorithms of the protocol can handle process failures and network partitioning. The experiment results of the implemented protocol in a local area network of workstations have demonstrated that its performance is better than any existing solutions in the same environment, especially, for achieving message total ordering and atomic (safe) delivery.

Maintaining a consistent state is crucial for cooperative work in autonomous and decentralized systems (ADS). This is achieved through reliable communication protocols in a group of autonomous components. Many existing protocols are quite expensive and not very suitable for the ADS. The paper presents a logical token ring based group multicast protocol for the service of decentralized action manage systems. Unlike previous token based algorithms, we assign a virtual identity to each of the processes executing in the autonomous components in an increasing order so as to form a logical ring. The protocol ensures total ordering and atomicity of multicast messages in the presence of the component failures. The total order is achieved by placing a sequence number in each multicast message. A token process implicitly multicasts one such ordered message and transfers the token to the next process on the ring, hence, reducing the synchronous overhead and preventing possible token lose problem. With a minimal number of control messages, the protocol guarantees that all nonfaulty processes belonging to the same group will observe a consistent view of ordered events affecting all cooperative components in the group. The efficient recovery algorithms can handle the member failures, dynamic groups, group partitions and merges.>

Type-specific locking is designed to increase performance of distributed transactions by allowing competing transactions to concurrently alter shared objects concurrently, provided their changes are commutative. When one of the set of compatible transactions commits or aborts, a problem arises due to the indeterminacy of the alterations of the others. A tree of nineteen solutions to the problem has been investigated. Given the necessary support by the underlying architecture, this tree can be pruned severely. The problem and set of approaches came to the authors' attention during design for type-specific locking in PROFEMO, an operating system for a local area network that provides a location-independent object environment and built-in mechanisms for transaction control and recovery. A description is given of the problem, the possible solutions, and the arguments that allow the pruning. Testbed results are not yet available, since type-specific locking has not yet been implemented at the time of the initial tests of the PROFEMO system.>

The following paper is to present a test and reconfiguration strategy for fault-tolerant VLSI processor systems. This is accomplished with respect to the requirements imposed by the VLSI technology. The proposed concept is exemplified by a model composed of four microprogrammable processors each with a local memory. The test strategy of a gradually expanding hardcore is applied where the central hardcore consists of a small test unit of low complexity. This test unit enables each processor to diagnose autonomously its data path structure and its associated local memory. A particular reconfiguration scheme is proposed for these components. It is implemented at microprogram level. As a result, compared with other fault-tolerance techniques, system reliability is considerably improved.