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Recently collaborative tagging has received great attention as a public effort to create and share annotations on the Web pages. In this paper, we conducted an empirical study on how this user added descriptions associated with Web resources can be used to enhance the existing Web search paradigm. Comprehensive experiments have been performed on data collected from delicious, one of the most popular collaborative tagging Web site. Some useful conclusions on the usage of different tags have been drawn from our data analysis. Based on these insights, we proposed an innovative tag enhanced exploratory Web search framework

Well engineered Web based courseware and exercises provide flexibility and added value to the students, which goes beyond the traditional text book or CD-ROM based courses. The Multibook project explores the boundaries of customized learning materials by composing learning trails dynamically as learners have set their profile to access a course. In this paper we first give an overview of the core project ideas and illustrate them along our Software Engineering course. Then we present a novel extension to the project's exercise environment with a graph editing component that particularly fits the needs of structure-related assignments.

Middleware forms such as CORBA and DCOM provide standard component interfaces, interaction protocols and communication services to support interoperability of object-oriented applications operating in heterogeneous and distributed environments. General-purpose services and facilities foster re-use and help reduce development costs. Yet the degree of automation of the software development process is limited to the generation of skeleton and stub code from component interface specifications given in a common interface definition language (IDL). This is mainly due to the fact that the expressiveness of current IDLs is limited to the specification of type and operation signatures. Important properties of crucial components of security-, safety-critical or reactive applications such as object behavior, timing or synchronization constraints cannot be documented formally, let alone checked automatically. In this paper, we continue developing solutions for adding specifications of semantic properties to component interfaces and automatically synthesizing code that instruments corresponding semantic checks. Independently from the concrete syntax and semantics of such specification elements, we present a collection of design patterns that allow the designer to seamlessly integrate the synthesized code with the code frames generated by standard IDL compilers. We study these approaches along the concrete example of extending CORBA IDL with synchronization constraints and we evaluate several implementations, solely based on standardized features of the CORBA standard.

IT experts expect open distributed processing to become the predominant computing infrastructure in the late nineties. All computer supported work places of large enterprises and organizations will then be networked and will be integrated into cross-regional and cross-sector business and information processes. The size and complexity of such applications, the local autonomy, distribution and heterogeneity of participating subsystems, and their asynchronous interaction, however, require new architectures, strategies, and tools for their technical management. In previous work we placed a production rule interpreter into the monitoring, decision, control action loop to provide flexible, operational semantics of well-understood management policies. In this article we extend this work in two directions. First we map the structure and dynamic behavior of policies into a graph representation. This semantic representation enables a systematic prediction of the effects of policy executions and allows for a better impact analysis in case of policy changes. Then we introduce a declarative event definition mechanism. It supports a causal and temporal correlation of individual events and serves to instantiate and adapt a predefined generic event handler to the specific needs of the actual management application. Such event handlers join in the interaction between monitoring agents and policy interpreter. By event correlation they may reduce the number of events triggering management actions significantly and help to filter secondary events.

A computing architecture enabling economical safety licensing of software embedded in safety-critical technical systems is defined. The architecture relies on mature methods and technology only. In particular, it includes a highly ergonomic but rigorous validation method, called diverse back translation. For safety-related program controlled electronic systems, safety licensing of software is extremely critical, since it is far from being as dependable as hardware. The presented approach deviates from classical construction and validation techniques by enforcing the re-use of pre-engineered and verified off-the-shelf application-oriented standard software function modules and by employing a graphical programming paradigm.

The formal semantics of a prototyping language for hard real-time systems, PSDL, is given. PSDL provides a data flow notation augmented by application-orientation timing and control constraints to describe a system as a hierarchy of networks of processing units communicating via data streams. The semantics of PSDL are defined in terms of algebraic high-level Petri nets. This formalism combines algebraic specifications of abstract data types with process and concurrency concepts of Petri nets. Its data abstraction facilities are used to define the meaning of PSDL data types, while high-level Petri nets serve to model the casual and timing behavior of a system. The net model exposes potential concurrency of computation and makes all synchronization needs implied by timing and control constraints explicit and precise. Time is treated as state of clocks, and clocks are modeled as ordinary system components. The net semantics provides the basis for applying analysis techniques and semantic tools available for high-level Petri nets.>

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Four new approaches for coping with strict timing constraints as encountered in industrial process control applications are presented. For each node in a distributed system, an asymmetrical two-processor architecture capable of guaranteeing response times is employed. One processor in each node is dedicated to the kernel of a real-time operating system. Its three reaction levels are constructively described by outlining their functional units and control procedures. Contemporary real-time computers are unable to manipulate external parallel processes simultaneously, and their response times are generally unpredictable. It is shown that these problems can be solved by endowing the node computers with novel process peripherals. They work in parallel and perform I/O operations precisely at user-specified instants. To cope with a transient overload of a node resulting from an emergency situation, a fault tolerant scheme that handles overloads by degrading the system performance gracefully and predictably is used. The scheme is based on the concept of imprecise results and does not utilize load sharing, which is usually impossible in industrial process control environments.>