Universität Stuttgart
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Item Open Access Security Tools 7: Paßwörter - ein ewiges Problem?(1997) Lehle, Bernd; Reutter, OliverUnsere bisherigen Artikel beschäftigten sich hauptsächlich mit Dingen, über die sich ein Systembetreuer Gedanken machen muß. Nun kommen wir zu einem Thema, das wirklich alle Benutzer angeht und bei dem jeder Benutzer durch leichtfertiges Verhalten Sicherheitslücken schaffen kann. Es ist daher nötig, daß diese Informationen an alle Benutzer weitergegeben werden.Item Open Access A protocol for preserving the exactly-once property of mobile agents(1997) Rothermel, Kurt; Straßer, MarkusMobile agents are autonomous objects that can migrate from node to node of a computer network. Mobile agent technology has been proposed for various application areas, including electronic commerce, systems management and active messaging. Many of these applications - especially those for electronic commerce - require agents to be performed 'exactly once', independent of communication and node failures. In other words, once a mobile agent has been launched, it must never be lost before its execution is finished. Moreover, each 'portion' of the agent performed at the visited nodes is performed exactly once. Due to the autonomy of mobile agents, there is no 'natural' instance that monitors the progress of an agent's execution. As a result of that agents may be blocked due to node crashes or network partitioning even if there are other nodes available that could continue processing. In this paper, we will describe a protocol that ensures the exactly once property of agents and additionally reduces the blocking probability of agents by introducing so-called observer nodes for monitoring the progress of agents. This protocol is based on conventional transactional technology, such as defined by X/Open DTP or CORBA OTS. It is implemented in the Mole, a mobile agent system developed at Stuttgart University.Item Open Access Languages, methods, and tools for software specification(1989) Ludewig, JochenSpecification systems consist of methods, languages, and tools; the languages may be more or less formal. In this paper, the general ideas of semi-formal specification systems are presented, and some examples are shown.Item Open Access Demonstration of supercomputing activities(1996) Geiger, Alfred; Wierse, Andreas; Helf, Clemens; Schmidt, Thomas; Warendorf, Katina; Küster, Uwe; Loebich, Isabel; Lepper, JürgenDuring the inauguration of HLRS a broad variety of supercomputing-activities was demonstrated. As HLRS is involved in the development of Software for supercomputers as well as in their usage, the demos concentrated on the development of novel simulation-codes in the field of Computational Fluid Dynamics, the software-tools which are necessary for the developper and on the presentation of typical applications from engineering in the VR-lab.Item Open Access Extending the relational algebra to capture complex objects(1989) Mitschang, BernhardAn important direction in database research for non-standard applications (e.g. engineering or design applications) deals with adequate support for complex objects. Without doubt, the provision of network structures and shared subobjects as well as support for dynamic object definition and appropriate manipulation facilities is urgently needed for natural and accurate modeling as well as for efficient processing of the applications' objects. These concepts are the major concern of the molecule-atom data model (MAD model) and its molecule algebra which is introduced in this paper. They make the model stand out compared to the relational model and even to models limited to hierarchical and statically defined complex objects. By means of the molecule algebra a precise and complete specification of one conceivable kind of complex object processing and its inherent semantics is provided. Furthermore, this algebra is used as a sound basis to express the semantics of the high level query language MOL (molecule query language) that is able to deal with complex objects in a descriptive manner.Item Open Access Practical methods and tools for specification(1987) Ludewig, JochenThis is a course on specification. Since it is based on experiences in the field of software engineering. It applies primarily to software specifications. Many observations and reports indicate, however, that, from specification aspects, there is not much difference between information processing systems in general and software in particular. Therefore, most of this course applies also to system specification. In the first chapter, some fundamentals are discussed. These include the life cycle model and the distribution of costs over the various activities, some definitions, and a rationale for semi-formal specification. The second chapter provides a general outline of a specification system, whose desirable properties are deduced from the qualities of good specifications. In the third chapter, we present some typical specification systems. The primary goal is to show some typical features of such systems rather than to describe them in detail. The fourth chapter addresses management aspects. In chapter 5, some general conclusions are drawn. The appendix (chapter 6) contains a bibliography on specification, and a list of suppliers.Item Open Access SQL/XNF - processing composite objects as abstractions over relational data(1993) Mitschang, Bernhard; Pirahesh, Hamid; Pistor, Peter; Lindsay, Bruce; Südkamp, NorbertAn extension to SQL, called the SQL extended normal form (XNF), is discussed. It enhances relational technology by a composite object facility, which comprises not only extraction of composite objects from existing databases but also efficient navigation and manipulation facilities provided by an appropriate application programming interface. The language itself allows sharing of the database among normal form SQL applications and composite object applications. It provides proper subsetting of the database and subsequent structuring, exploiting subobject sharing and recursion, all based on its powerful composite object constructor concept, which is closed under the language operations. XNF is integrated into the relational framework, thus benefiting from the available technology such as relational engine and query optimization.Item Open Access Software Engineering und CASE - Begriffserklärung und Standortbestimmung(1991) Ludewig, JochenCASE-Tools werden heute als wichtige Mittel der Leistungs- und Qualitätssteigerung im Software Engineering betrachtet. Diese Einschätzung ist richtig, wenn sie mittel- und langfristig verstanden wird; sie ist falsch, wenn man erwartet, rasche Hilfe zu bekommen, die Versäumnisse in der Methodik und Schulung ausgleicht. Die heute angebotenen Werkzeuge weisen charakteristische Mängel auf, die - entgegen den Ankündigungen - ihren durchgehenden Einsatz sehr schwer machen. Trotzdem kann unter bestimmten Voraussetzungen, auch organisatorischen, die Qualität des Entwicklungsprozesses tatsächlich erhöht werden. Diese Verbesserung wirkt sich auch auf die Produktivität aus.Item Open Access Technisch-Wissenschaftliches Rechnen mit modernen PCs(1996) Helf, Clemens; Küster, Uwe; Zürn, ManuelaIntel hat im vergangenen Jahr mit dem Pentium Pro den ersten PC-Prozessor auf den Markt gebracht, der hohe Leistung, PC-Funktionalität und -Kosten miteinander vereinigen soll. Er wird in Home Computern, Workstations, Servern und Supercomputern stecken. Seine nominelle Leistung ist so hoch wie die einer CRAY-1, das Memory wenigstens das Achtfache. In der Vergangenheit waren aufwendige numerische Berechnungen an Supercomputer gebunden, danach eine Domäne der Workstations. Wird der PC in Zukunft die Alternative im Technisch-Wissenschaftlichen Rechnen?Item Open Access Flinke Prototypen : der SFB 374 stellt sich vor(1997) Kunz, Christoph; Rantzau, Dirk; Sigel, Julian; Eschl, Johannes; Keller, BerndSeit dem 1. Oktober 1994 existiert der Sonderforschungsbereich 374 Entwicklung und Erprobung innovativer Produkte - Rapid Prototyping - an der Universität Stuttgart. Der SFB beschäftigt sich ganz allgemein mit der Entwicklung von Methoden zur einheitlichen Darstellung von Prototypwissen, der Entwicklung von Verfahren zur schnellen Erzeugung virtueller und physischer Prototypen sowie der Kopplung beider Bereiche durch neu zu entwickelnde Kooperations- und Kommunikationsmodelle. Am RUS ist das Teilprojekt D2, das sich mit der Simulation und Visualisierung technisch-physikalischer Vorgänge beschäftigt, entstanden.