Hermann A. Maurer

Stabbing line segments

An algorithm for the geometric problem of determining a line (called a stabbing line) which intersects each ofn given line segments in the plane is presented. As a matter of fact, the algorithm computes a description of all stabbing lines. A purely geometric fact is proved which infers that this description requiresO(n) space to be specified. Our algorithm computes it inO(n logn) time which is optimal in the worst case.Using the description of the stabbing lines, we are able to decide inO(logn) time whether or not a specified line is a stabbing line. Finally, the problem of maintaining the description of all stabbing lines while inserting and deleting line segments is addressed.

Finding extreme points in three dimensions and solving the post-office problem in the plane

Abstract This paper describes an optimal solution for the following geometric search problem defined for a set P of n points in three dimensions: Given a plane h with all points of P on one side and a line l in h, determine a point of P that is hit first when h is rotated around l. The solution takes O(n) space and O(log n) time for a query. By use of geometric transforms, the post-office problem for a finite set of points in two dimensions and certain two-dimensional point location problems are reduced to the former problem and thus also optimally solved.

Chain code picture languages

A picture is a connected set of axis parallel unit lines from the Cartesian plane considered as a square grid. A word over the alphabet {l,r,u,d} is a picture description in the sense that it represents a traversal of a picture where the interpretation of the symbols l,r,u,d is: l — go (and draw) one unit line to the left of the current point; r,u, and d are interpreted analogously with “left” replaced by “right”, “up”, and “down”, respectively. This is one of the chain codemodels.

A space-optimal solution of general region location

Abstract In 1979 Kirpatrick obtained a practically feasible algorithm for planar region location working in linear space and logarithmic time, provided the regions are bounded by straight line segments. No algorithm requiring only linear space and log-polynomial time was known, so far, for general planar region location, i.e. for the case where regions are bounded by curves more complicated than straight line segments. As main result of this paper such an algorithm is presented.

DynamIcons as dynamic graphic interfaces: Interpreting the meaning of a visual representationPA

Abstract Iconic interfaces in operating systems and hypermedia knowledge bases have become the default standard. The content, purpose, or function implied by icons may be enhanced by making them more dynamic. Dynamlcons can use representational, abstract, or symbolic graphics to convey the categorical or functional information or inferences and implications about its referent. Conveying more information in the design of icons can make iconic interfaces even more efficient.

Increasing the similarity of EOL form interpretations

Ordinary interpretations of EOL forms permit the omission of productions and the replacement of different occurrences of the same symbol in a production by different symbols. This drastically weakens the relation between the structure of an interpretation and its underlying EOL form. We claim that by using the notion of X -uniformity and cc -interpretation this drawback can be overcome.

Authoring systems for computer assisted instruction

Computer Assisted Instruction (CAI) has been hailed in the past as final answer to most teaching situations just about as often as it has been termed a failure. The truth is that CA1 has not achieved the big breakthrough sometimes expected, sofar, but has found a growing number of successful niches. However, things are starting to change dramatically: with the spreading of high-power yet inexpensive personal computers suitable for running educational software, the continuing growth of data-networks for e.g. the distribution of such courseware and a number of other contributing factors to be detailed below, a rapid expansion of CA1 applications can be safely predicted.

Good OL forms

SummaryFor the study of grammatical similarity of L systems the notion of an L form has been introduced recently. In particular, complete forms and their generalizations, good forms, have been studied. In this paper the ramification of these notions as applied to OL systems is investigated.

Managing Editor’s Column

Dear Readers: It is with pleasure that I present to you this month’s extensive issue of 16 excellent papers that show the range of subjects covered by J.UCS. The issue also shows the international flavour of our journal: the contributions come from 16 countries! Those are, in alphabetical order: Australia, Austria, China, Czech Republic, Egypt, Greece, India, Iran, Italy, Japan, New Zealand, Pakistan, The Netherlands, Tunisia, United Arab Emirates and the USA! I am sure you will find a number of contributions that will interest you. Please continue to help J.UCS to grow, by submitting high quality papers and recommending our journal to your friends. Note also that Volume 10 (2004) is now also available in printed form, with 1733 pages (!) the largest volume so far! To order the archive edition, please fax or send us the order form from http://www.jucs.org/jucs subscription/print.html Finally, I’d like to draw your attention to the launch of two new journals: Journal of Universal Knowledge Management (http://www.jukm.org) and Journal of Universal Science and Technology of Learning (http://www.justl.org) which will be published by the same team as is responsible for the publication of J.UCS. Because of the immensely growing interest for publication in J.UCS, we have lately not been able to provide the necessary publication space for all authors and guest editors interested in publishing their articles in our journal. To alleviate this problem and to provide new platforms for the dynamic areas of Knowledge Management and E-Learning, the new journals were established and will be opened for submissions in August 2005 and September 2005, respectively. If you are interested in publication, membership of the editorial board or any other aspect connected with the new journals, please contact the two managing editors, namely Klaus Tochtermann (J.UKM) at ktochter@know-center.at or Heinz Dreher (J.USTL) at hdreher@iicm.edu. We look forward to hearing from you! For now enjoy reading this ’special’ regular issue!

Bijective A-transducers

In this paper we study bijective a-transducers. We derive necessary and sufficient conditions on pairs of regular sets (R,S) such that a bijective a-transducer, mapping R cnto S exists. The results obtained allow the systematic construction of an a-transducer, mapping a set R onto a set S bijectively for surprisingly different regular sets R and S.