Dr. Hans Jürgen Ohlbach


Reasoning on the Web
Slim Abdennadher, Jose Julio Alves Alferes, Grigoris Antoniou, Uwe Aßmann, Rolf Backofen, Cristina Baroglio, Piero A. Bonatti, Francois Bry, Wlodzimierz Drabent, Norbert Eisinger, Norbert E. Fuchs, Tim Geisler, Nicola Henze, Jan Maluszynski, Massimo Marchiori, Alberto Martelli1, Sara Carro Martinez, Wolfgang May, Hans Jürgen Ohlbach, Sebastian Schaffert, Michael Schröder, Klaus U. Schulz, Uta Schwertel, and Gerd Wagner

Automated reasoning is becoming an essential issue in many Web systems and applications, especially in emerging Semantic Web applications. This article first discusses reasons for this evolution. Then, it presents research issues currently investigated towards automated reasoning on the Web and it introduces into selected applications demonstrating the practical impact of the approach. Finally, it introduces a research endeavor called REWERSE (cf. http://rewerse.net) recently launched by the authors of this article which is concerned with developing automated reasoning methods and tools for the Web as well as demonstrator applications.

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Fuzzy Time Intervals and Relations - The FuTIRe Library
Hans Jürgen Ohlbach

The FuTIRe library is a collection of classes and methods for representing and manipulating fuzzy time intervals and relations between them. Time intervals like `tonight', which are usually not very precise, can be modelled as fuzzy sets. But this causes the problem that the relations between points and intervals and between two intervals, which are usually very trivial, become very complex when the intervals are fuzzy sets. Moreover, there are many different possibilities to define such relations. In FuTIRe it is not only possible to represent fuzzy time intervals, but one can define customized fuzzy point-interval and interval-interval relations. These relations can even yield fuzzy values when the intervals are in fact crisp. As an example, consider a database with, say, a cinema timetable, and you query the timetable ``give me all performances ending before midnight''. The usual `before' relation will exclude the performances ending a second after midnight. With the fuzzy before relation in FuTIRe you can get instead of a sharp drop to 0 at midnight decreasing fuzzy values after midnight, and these can be used to order the results of the query. FuTIRe is an open source C++ library.

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Conference Version (PDF 171K), Appears in the proceedings of the TIME 04 conference.

The Role of Labelled Partitionings for Modeling Periodic Temporal Notions
Hans Jürgen Ohlbach

The key notion for modelling calendar systems is the notion of {\em a partitioning of the real numbers}. A partitioning of \Real\ splits the time axis into a finite or infinite sequence of intervals. Basic time units like seconds, minutes, hours, days, weeks, months, years etc.\ can all be represented by finite partitionings of \Real. Besides the basic time units in calendar systems, there are a lot of other temporal notions which can be modelled as partitions: the seasons, the ecclesiastical calendars, financial years, semesters at universities, the sequence of sunrises and sunsets, the sequence of the tides, the sequence of school holidays etc. In this paper a formalization of periodic temporal notions by means of {\em labelled partitionings} of \Real\ is presented. Many natural language temporal expressions can be mapped to operations on partitionings of their labels.

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Conference Version (PDF 102K), Appears in the proceedings of the TIME 04 conference.

Calendrical Calculations with Time Partitionings and Fuzzy Time Intervals
Hans Jürgen Ohlbach

This paper presents a piece in a big mosaic which consists of formalisms and software packages for representing and reasoning with everyday temporal notions. The kernel of the mosaic consists of several layers. At the bottom layer there are a number of basic datatypes for elementary temporal notions. These are time points, crisp and fuzzy time intervals and partitionings for representing periodical temporal notions like years, months, semesters etc. Partitionings can be arranged to form `durations' (e.g. `2 semester and 1 month'). Each formalism in the bottom layer comes with its own functions and relations. The second layer is presented in this paper. It contains a number of basic functions which use time points, intervals, partitionings and durations simultaneously. The functions are introduced and motivated with temporal expressions in natural language. The third layer, which is not presented in this paper, uses the functions and relations of the lower layers as building blocks in a specification language for specifying complex temporal notions. The whole mosaic contains a number of other formalisms, in particular a representation of calendar systems, and various databases with information about temporal notions.

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Active Event Databases for Evaluating Temporal Notions
Jan Dünnweber and Hans Jürgen Ohlbach

This paper presents WebTNDB (Web Temporal Notions Database), a system for representing and administering event data. Events are described by various attribute-value pairs where the values are nodes in an ontology network. One of the attributes gives the time when the event happened. The event database is to be used for evaluating temporal notions referring to events. An example could be `after the Rolling Stones concert in Frankfurt in 1990'. The system has a graphical user interface for querying the database and for administering the ontology network. We describe the data model, the ontology network, the graphical query editor and the mapping to SQL databases. Special focus is on the Java implementation and how it can exploit the aggregate power of the utilized machines to achieve performant lookups.

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Last Modified: Friday, 07-May-2004 09:38:00 CEST