Focus of attention in an activity-based scheduler

Earlier research in job shop scheduling has demonstrated the advantages of opportunistically combining order-based and resource-based scheduling techniques. An even more flexible approach is investigated where each activity is considered a decision point by itself. Heuristics to opportunistically select the next decision point on which to focus attention (i.e., variable ordering heuristics) and the next decision to be tried at this point (i.e., value ordering heuristics) are described that probabilistically account for both activity precedence and resource requirement interactions. Preliminary experimental results indicate that the variable ordering heuristic greatly increases search efficiency. While least constraining value ordering heuristics have been advocated in the literature, the experimental results suggest that other value ordering heuristics combined with our variable-ordering heuristic can produce much better schedules without significantly increasing search

Expected performance of m-solution backtracking

This paper derives upper bounds on the expected number of search tree nodes visited during an m-solution backtracking search, a search which terminates after some preselected number m problem solutions are found. The search behavior is assumed to have a general probabilistic structure. The results are stated in terms of node expansion and contraction. A visited search tree node is said to be expanding if the mean number of its children visited by the search exceeds 1 and is contracting otherwise. It is shown that if every node expands, or if every node contracts, then the number of search tree nodes visited by a search has an upper bound which is linear in the depth of the tree, in the mean number of children a node has, and in the number of solutions sought. Also derived are bounds linear in the depth of the tree in some situations where an upper portion of the tree contracts (expands), while the lower portion expands (contracts). While previous analyses of 1-solution backtracking have concluded that the expected performance is always linear in the tree depth, the model allows superlinear expected performance

Proceedings of the NASA Conference on Space Telerobotics, volume 1

The theme of the Conference was man-machine collaboration in space. Topics addressed include: redundant manipulators; man-machine systems; telerobot architecture; remote sensing and planning; navigation; neural networks; fundamental AI research; and reasoning under uncertainty

Applying the Engineering Statechart Formalism to the evaluation of soft real-time in operating systems : a use case tailored modeling and analysis technique

Multimedia applications that have emerged in recent years impose unique requirements on an underlying general purpose operating system (GPOS). The suitability of a GPOS for multimedia processing is judged by its soft real-time capabilities. To date, the question of how these capabilities can be assessed has scarcely been addressed: this is a gap in GPOS research. By answering questions on the impacts of the Interrupt Handling Facility (IHF) on the overall soft real-time capabilities of a GPOS, this thesis contributes to the filling of this blank space. The Engineering Statechart Formalism (ESF), a use case tailored formal method of modeling real-world OS, is syntactically and semantically defined. Models of the IHF of selected real-world operating systems are then created by means of this technique. As no appropriate real-time concept fitting the goals of this thesis as yet exists, a suitable definition is constructed. By projecting this system-wide idea to the interrupt subsystem, specific indicators for this subsystem are erived. These indicators are then evaluated by applying formal techniques such as graph-based analysis and temporal logic model checking to the ESF models. Finally, the assertions derived from this evaluation are interpreted with respect to their impacts on real-time multimedia processing in different general purpose operating systems.Multimedia-Anwendungen haben in den letzten Jahren weite Verbreitung erfahren. Solche Anwendungen stellen besondere Anforderungen an das Betriebssystem (BS), auf dem sie ausgeführt werden. Insbesondere Echtzeitfähigkeiten des Betriebssystems sind von Bedeutung, wenn es um seine Eignung für Multimedia-Verarbeitung geht. Bis heute wurde die Frage, wie sich diese Fähigkeiten konkret innerhalb eines BS manifestieren, nur unzureichend untersucht. Die vorliegende Arbeit leistet einen Beitrag zur Füllung dieser Lücke in der BS-Forschung. Die Effekte des Subsystems zur Unterbrechungsbehandlung in BS auf die Echtzeitfähigkeit des Gesamtsystems werden detailliert auf Basis von Modellen dieses Subsystems in verschiedenen BS analysiert. Um eine formale Auswertung zu erlauben, wird eine auf den Anwendungsfall zugeschnittene formale Methode zur BS-Modellierung verwendet. Die spezifizierte Syntax und Semantik dieses Engineering Statechart Formalism (ESF) basieren auf dem klassischen Statechart-Formalismus. Da bislang kein geeigneter Echtzeit-Begriff existiert, wird eine konsistente Definition hergeleitet. Durch die Abbildung dieser sich auf das Gesamtsystem beziehenden Eigenschaft auf die Unterbrechungsbehandlung werden spezifische Indikatoren für dieses Subsystem hergeleitet. Die Ausprägungen dieser Indikatoren für die verschiedenen untersuchten Betriebssyteme werden anhand formaler Methoden wie graphbasierter Analyse und Temporal Logic Model Checking ausgewertet. Die Interpretation der Untersuchungsergebnisse liefert Aussagen über die Effekte der Implementierung der Unterbrechungsbehandlung auf die Echtzeitfähigkeit der untersuchten Betriebssysteme bei der Verarbeitung von multimedialen Daten