Gerhard Köstler

Preference SQL: design, implementation, experiences

Current search engines can hardly cope adequately with fuzzy predicates defined by complex preferences. The biggest problem of search engines implemented with standard SQL is that SQL does not directly understand the notion of preferences. Preference SQL extends SQL by a preference model based on strict partial orders (presented in more detail in the companion paper [Kie02]), where preference queries behave like soft selection constraints. Several built-in base preference types and the powerful Pareto operator, combined with the adherence to declarative SQL programming style, guarantees great programming productivity. The Preference SQL optimizer does an efficient re-writing into standard SQL, including a high-level implementation of the skyline perator for Pareto-optimal sets. This pre-processor approach enables a seamless application integration, making Preference SQL available on all major SQL platforms. Several commercial B2C portals are powered by Preference SQL. Its benefits comprise cooperative query answering and smart customer advice, leading to higher e-customer satisfaction and shorter development times of personalized search engines. We report practical experiences ranging from m-commerce and comparison shopping to a large-scale performance test for a job portal.

Fixpoint iteration with subsumption in deductive databases

Declarative languages for deductive and object-oriented databases require some high-level mechanism for specifying semantic control knowledge. This paper proposes user-supplied subsumption information as a paradigm to specify desired, prefered or useful deductions at the meta level. For this purpose we augment logic programming by subsumption relations and succeed to extend the classical theorems for least models, fixpoints and bottom-up evaluation accordingly. Moreover, we provide a differential fixpoint operator for efficient query evaluation in deductive databases. This operator discards subsumed tuples on the fly. We also exemplify the ease of use of this programming methodology. In particular, we demonstrate how heuristic AI search procedures can be integrated into deductive databases in this way.

The differential fixpoint operator with subsumption

Declarative languages for deductive and object-oriented databases require some high-level mechanism for specifying semantic control knowledge. This paper proposes user-supplied subsumption information as a paradigm to specify desired, prefered or useful deductions at the meta level. For this purpose we augment logic programming by subsumption relations and succeed to extend the classical theorems for least models, fixpoints and bottom-up evaluation accordingly. Moreover, we provide a differential fixpoint operator for efficient query evaluation. This operator discards subsumed tuples on the fly. We also exemplify the ease of use of this programming methodology. In particular, we demonstrate how heuristic AI search procedures can be integrated into logic programming in this way.

Client-Server Optimization for Multimedia Document Exchange

The success of the World Wide Web is boosting the development of multimedia database systems and their integration into the internet. For the documents stored and exchanged in the Web there are many multimedia data formats di ering in aspects such as resolution, sampling rate, and compression. Furthermore there is a large variety of Web browsers, the data formats they support, and their network access. Thus storage servers have to store and proxy servers have to transfer many di erent formats. However, the data formats are not independent from each other but interrelated by conversion tools. There is a large number of alternatives for storage and proxy servers to store some formats or to transfer them via the network and to compute the remaining ones by applying conversion tools. To determine an optimal choice is a nontrivial optimization problem and is subject to changes of the parameters such as query pro le, available disk storage, and network bandwidth. We examine the outlined optimization problem in the context of objectoriented databases and illustrate our approach by a practical real-world application.

Fixpoint Evaluation with Subsumption for Probabilistic Uncertainty

The deep complexity of uncertain data modelling has resisted to general solutions so far. Instead, a diversity of modelling approaches has been proposed over the years, but few systems actually have been built. The DUCK calculus is one recent ambitious rule-based attempt to model uncertainty on the grounds of established probability theory as typically used e.g. in medical diagnosis. This paper describes how deductive database technology can be exploited for prototyping of a system for uncertain reasoning.

Taxonomic and uncertain integrity constraints in object-oriented databases—the TOP approach

We present a coherent modeling and reasoning methodology to extend object-oriented databases towards taxonomic and uncertain integrity constraints. Our so-called TOP database model enriches current ISA-hierarchies by more general t-classes to improve conceptual modeling. The t-classes themselves are then integrated with probabilistic constraints to express uncertainty. We give an efficient algorithm for checking the modeling-consistency of a probabilistic knowledge base. As a typical application domain for TOP, we exemplify how various aspects of a portfolio management system can be modeled. We also demonstrate that recent probabilistic inference methods, relying on a careful interaction between taxonomic and uncertain knowledge, can be applied in this context.

Die Lernsoftware auf CD-ROM

Wir wollen einen Vorgeschmack auf das gesamte HTML-basierte Kursmaterial auf der CD-ROM vermitteln. Hier ist zuerst ein Bildschirm-Dump des Hauptmenus abgebildet.

Implementierung der Relationenalgebra

Wir haben uns eingangs bereits den strukturellen Aufbau eines DB-Systems uberlegt. Fur das folgende ist eine Detaillierung der physischen DB-Organisation notwendig.

Der ODMG-93-Standard

Wichtige Standardisierungsbemuhungen im Bereich objektorientierter (und verteilter) Systeme finden im Rahmen der Object Management Group (OMG) statt, in der uber 500 Firmen und Institutionen vertreten sind.

Das Entity-Relationship-Modell

Jedes DB-System stutzt sich auf ein Datenmodell. Ein Datenmodell ist ein (mathematischer) Formalismus, der aus n n neiner Notation zur Schemabeschreibung (DDL) und aus n n neinem Satz von Operationen zur DB-Manipulation (DML) besteht.