Kolloquium/Ringvorlesung des Graduiertenkolleg Wissensrepräsentation

We assess syntactic and semantic issues of providing information to large applications in terms of integration and interoperation levels for technologies ranging from centralized and federated databases, through warehousing, mediation, to knowledge repositories. We draw conclusions for effective architectures, community acceptance, and research issues to be addressed.

Extended Abstract

The success of database technologies and the Internet has lead to an explosion of available information. For any given purposes we can data about every topic, from many points of view, and from a wide variety of sources. There is greatly increased value to assimilating the data together, since the relationships among previously disjoint data provides novel insights and hence information that was not available before. Early database concepts to support such an assimilation were based on having large, centralized databases, and pushing all data to such a central repository. Scalability issues led to concepts of federated databases, which shared a schema and enabled distributed search. Integration of data was achieved through interoperation at the level of communication technology. The results mirrored the sources exactly, and any semantic relationships or mismatches had to be handled by the applications.

Current warehouse technology is a direct descendant of that direction, but now formalizing the central database as an integrated copy, reducing the need for concurrent interoperation. Warehouses enabled transformations of the source to make it easier to search and drill down within the accumulated data. From the point-of-view of a using application, having all possibly interesting data instantly available and together is very attractive. The low cost of storage motivates such collections, although performance remains an issue, since access times of disk storage have not increased as much. The major cost of this approach is in keeping the warehouse up-to-date. For data sources that change frequently the cost of shipping incremental updates to the warehouse and inserting it correctly is high, and read-to-write ratios for large data collections will be low as well, reducing the benefit/cost ratio. Since sources may differ in semantics, the required global resolution of their differences is also an ongoing task.

Moving to information intgration through interoperation among data sources is an alternate approach to deal with excessive data volumes to obtain information. Integration of data is provided in servers. Only descriptive information and processing knowlegde is stored in the servers. Applications are expected to deal with higher level concepts and delegate selection and summarization. The concept of intelligent mediators hypothesizes that the required knowledge is domain specific, and can reside neither in the sources, nor be effectively delegated to the individual applications. Since abstractions and summaries change slower than the data collected in the sources, the transmission requirements between the mediators and the applications is less. The mediated architecture was predicated on using queries, both from the applications that required information and from the mediators, that required data from the sources. Integration occurs at two levels: a domain-specific mediator must integrate data from multiple sources, using shared concepts and metrics, while applications may access various mediators to obtain information from multiple domains that are semantically disjoint. The portions of a system must interoperate effectively since the linkages are dynamic. Caching may reduce the load for data transfer about active topics. Having substantial and persistent information caches leads topwards new architectures.

Knowledge repositories are a technology not yet well formalized today, to combine information interoperation with integration. A knowledge repository may use subscribe technology to obtain data, but let the applications obtain data via queries, or pull technology. In the model we foresee performance can be higher, since applications only need to pull integrated information from the repositories, while the sources publish and push information to the repositories. A higher level of intelligence, or prescience is needed, to define the content needed in such repositories. The sources should be dynamically accessible so that results can be questioned and validated. The scale of systems can be increased, since the transmission rates and connectivity demands are reduces with respect to the sources, and interoperability can focus on repository access. Resolution of semantic differences is performed when information is placed within the knowledge repositories.

The discussion up this point have used a three-level architectural model, although in any of the alternatives more levels have been contemplated and occasionally implemented. The high value and complexity of establishing routine linkages among related, but autonomous services might require a layer that is distinct in style >From repository services that are best when focusing on coherent domains.

Any increase in levels requires great care. The operational complexity, the likelihood of needing different standards for performance and representation among levels, induces costs and risks that may be high. The business models also become more difficult, since services as mediation and knowledge repositories require expert maintenance, who must be compensated. The lack of simple, incremental payment schemes on the Internet disables the initiation of information service providers. On the other hand, the acceptance of representation standards such as XML, the availability of transport middleware from many sources, and the expectations of the user community will provide motivations for progress in information integration and interoperation.

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Gio Wiederhold is an emeritus professor of Computer Science, Electrical Engineering, and Medicine at Stanford University, continuing part-time with ongoing projects and students. Since 1976 he has supervised 31 PhD theses in these departments. Current research topics in large-scale information systems include composition, access to simulations to augment decision-making capabilities, developing an algebra over ontologies and privacy protection in collaborative settings.

Wiederhold has authored and coauthored more than 350 publications and reports on computing and medicine, including an early popular Database Design textbook. He initiated knowledge-base research through a white paper to DARPA in 1977, combining databases and Artificial intelligence technology. The results led eventually to the concept of mediator architectures.

Wiederhold was born in Italy, received a degree in Aeronautical Engineering in Holland in 1957 and a PhD in Medical Information Science from the University of California at San Francisco in 1976. Prior to his academic career he spent 16 years in the software industry. His career followed computer technologies, starting with numerical analysis applied to rocket fuel, FORTRAN and PL/1 compilers, real-time data acquisition, a time-oriented database system, eventually becoming a corporate software architect.

He has been elected fellow of the ACMI, the IEEE, and the ACM. He spent 1991-1994 as the program manager for Knowledge-based Systems at DARPA in Washington DC. He has been an editor and editor-in-chief of several IEEE and ACM publications. Gio's web page is http://www-db.stanford.edu/people/gio.html.

Beschreibungslogiken sind eine Familie logischer Formalismen zur Repräsentation von konzeptuellem Wissen. Da es mit abstrakten logischen Mitteln schwierig ist, "`konkrete Eigenschafen"' von Objekten (wie z.B. deren Alter, Gewicht oder Größe) in adäquater Weise zu beschreiben, wurde die Erweiterung von Beschreibungslogiken um sogenannte konkrete Bereiche vorgeschlagen. In diesem Vortrag werden wir---nach einer allgemeinen Einführung in die Thematik der konkreten Bereiche---eine umfassende Analyse der Komplexität des Schließens in Beschreibungslogiken mit konkreten Bereichen vornehmen. Es zeigt sich, daß das Schließen mit ALC(D), der Erweiterung der grundlegenden Beschreibungslogik ALC um konkrete Bereiche, PSpace-vollständig ist, also nicht härter als in ALC selbst. Andererseits führt das Hinzunehmen von "`normalerweise harmlosen"' Ausdrucksmitteln wie azyklischen TBoxen zu einem drastischen Anstieg der Komplexität: Die resultierenden Logiken sind meist NExpTime-vollständig oder sogar unentscheidbar. Diese Härte- bzw. Unentscheidbarkeitsresultate setzen jedoch voraus, daß der konkrete Bereich bestimmte, relativ schwache Bedingungen erfüllt. Wir zeigen, daß es interessante konkrete Bereiche gibt, die diese Bedingungen nicht erfüllen. Dies führt zur Definition einer ausdrucksstarken intervall-basierten temporalen Beschreibungslogik, in der das Schließen entscheidbar ist.

The WITAS (vee-tas) UAV project is an ambitious research project with a focus on the development of information technology for unmanned aerial vehicles and it's combination with low-level control and hardware platforms. The long term goal of the project is the development of a fully autonomous unmanned helicopter which can be used in applications involving photogrammetry, surveillance and monitoring of traffic, and emergency services assistance. The project encompasses a variety of core functionalities and techniques such as prediction, planning, modeling scenes and events on the ground, use of those models for autonomous decisions, active vision, the design of deliberative/reactive architectures, GIS, simulation tools, multi-modal ground operator interfaces to the UAV and much more. In the talk, I will provide an overview of some of this work and the current state of the project. Recent progress will be demonstrated with a number of video sequences and simulation runs. In the talk I will focus on some of the interesting knowledge representation and architectural challenges in the project.

Patrick Doherty is a Professor in Computer Science at the Department of Computer and Information Science (IDA), Linköping University, Sweden. He is the head of the Artificial Intelligence and Integrated Computer Systems Division at IDA and the Knowledge Processing Laboratory. He is also President of the Swedish Artificial Intelligence Society.

Das Kontrollprogramm eines autonomen mobilen Roboters ist ein besonderes Stück Software. Roboteraktionen sollen einerseits durch schnelle Reflexe auf die Daten seiner Umgebungssensoren beeinflusst werden -- Kollisionsvermeidung bei schneller Fahrt ist ein Beispiel dafür. Andererseits soll der Roboter abstrakte, in Symbolform gegebene Benutzeraufträge ausführen, über vorliegende und asynchron einkommende symbolische Informationen schlussfolgern und planen, was eine Zeitlang dauern darf. Keiner der beiden Modi hat Vorrang vor dem jeweils anderen. Die Verarbeitung von Sensordatenströmen in kurzem Zeittakt und von symbolischer Information in langen Zeittakten muss geeignet gemischt werden.

Es existieren einige Beispiele solcher hybrider Roboterkontrollsysteme, doch klare Entwurfsprinzipien oder auch nur Erfolgsmaßstäbe dafür gibt es nicht. Der Vortrag führt in die Problemstellung ein und beschreibt dann die hybride Roboterkontrollarchitektur DD&P, die derzeit entwickelt wird. Im Detail behandelt er die Frage, wie ein in propositionaler Form vorliegendes Umgebungsmodell auf Basis der Sensordatenströme aktualisiert wird.

Der Vortrag stellt zunächst ein allgemeines Schema für die Kooperation und Koordination von Constraint-Lösern vor. Das System basiert auf einem einheitlichen Interface für die Löser, welches eine feinkörnige formale Spezifikation des Informations-Austauschs zwischen diesen ermöglicht. Der Kombinationsmechanismus für Constraint-Löser erlaubt weiterhin die Integration von deklarativen Sprachen in das Gesamtsystem und damit deren Erweiterung um Constraints. Der Vortrag demonstriert dies anhand der Beispiele einer logischen und einer funktional- logischen Sprache.

Die Mereologie ist ein Bereich der Metaphysik, in dem formale Methoden Eingang gefunden haben. Formale Methoden sind noch keine Garantie fuer eine fruchtbare theoretische Entwicklung. Ein Symptom, das auf das Misslingen einer Formalisierung eines philosophischen Gebiets hinweist, ist die Tatsache, wenn es nur formale Definitionen und Axiome aber keine nichttrivialen Theoreme gibt. Ein anderer Hinweis waere, wenn jeder auf diesem Gebiet arbeitende Autor seine eigene Formalisierung vortraegt, ohne dass es zu einer Standardisierung kommt, da keine Kriterien gefunden werden, die es erlauben, eine Formalisierung gegenueber einer anderen auszuzeichnen. In dem Vortrag werden Representationssaetze Mereologischer Systeme untersucht.

Thomas Mormann

Dept. of Logic and Philosophy of Science

University of the Basque County

Merging multiple sources information is an important problem in many areas such that databases integration systems, robotics, multi-agent systems, etc. The multiplicity of sources providing information often leads to contradictory information. Recently, aggregation operators of propositional knowledge bases have been defined to solve conflicts and to generate a consistent base as a result of merging. The first part of the talk presents a general approach to fuse prioritized bases. We show that fusion of propositional bases can be easily recovered in this setting. This encoding has two advantages: first, the result of merging is a prioritized base, hence the merging process can be decomposed and iterated in a coherent way. Moreover, it provides a syntatic counterpart of merging propositional bases. The second part of the talk provides a brief survey of a possibilistic handling of default rules. A set of default rules of the form, "generally, from a deduce b", is viewed as the family of possibility distributions satisfying constraints expressing that the situation where a and b is true has a greater plausibility than the one where a and "not b" is true. Different forms of nonmonotonic consequence relations that can be defined fom this family of possibility distributions will be presented. We also briefly show how they can be applied for modelling access control in health care domain.