Georg Lehrenfeld

A Distributed Implementation of Flat Concurrent Prolog on Multi-Transputer Environments

FCP is a general purpose concurrent logic programming language. We describe a distributed implementation of FCP on a multi-transputer environment based on the design of a parallel FCP machine.

Integrating a constraint solver into a real-time animation environment

Investigates the integration of an interactive constraint solver into an existing 2D real-time animation environment in order to achieve a better observability, traceability and stability of the individual graphical objects. We present two approaches for assigning constraints to the objects. The first approach assigns constraints to the objects when they are created, keeping them stable during their entire life-time. The second approach dynamically changes constraints before the computation of each frame. The investigation is based on our practical experience with the complete visual programming language Pictorial Janus and the parallel constraint solver Parcon.

Visual-textual prototyping of 4D scenes

3D-graphics are becoming popular in a steadily increasing number of areas such as entertainment, scientific visualization, simulation, and virtual reality. Despite this rapid growth the generation of animated 3D scenes is by no means trivial. Since animated 3D objects evolve over time the authors denote these objects as 4D. The article presents a novel approach to the rapid prototyping of 4D models. They introduce the AAL (Animated Agent Layer) system. AAL is an interpreter-based approach covering a textual (AAL-PR) as well as a visual command language (AAL-VL) for the specification of the dynamics in 4D scenes. AAL provides support for different levels of abstraction: primitives, structured objects, animated objects, and animated (autonomous) agents.

Visual modeling and 3D-representation with a complete visual programming language-a case study in manufacturing

The main goal of the article is to evaluate the suitability of visual programming languages, i.e., Pictorial Janus (K. Kahn and V. Saraswat, 1990), for the modeling of complex systems and their control strategies. These systems can be seen as networks of communicating objects. Objects select strategies for suitable actions based on incoming messages. Our field of investigation is in computer integrated manufacturing considering the example of a car manufacturing cell. This color sorting assembly buffer (CSAB) schedules jobs in queues. The jobs represent car bodies scheduled in feeder lines for the enameling. Feeder lines collect raw bodies to blocks. Blocks are bodies which are to be enameled by the same color. This organization decreases the cost of expensive change-over-times when changing colors at the enamelling. Blocks of bodies are dislocated from the queue and enameled successively. Contradictory system goals, such as minimizing color changes and preserving the sequence of incoming jobs, have to be regarded by appropriate control strategies. Due to the complexity of this (NP complete) problem and to real time requirements for online control there are no optimal strategies on hand. Consequently, suitable heuristics have to be developed. Often they are designed applying a trial-and-error method. A modeling framework has to support the rapid prototyping of these systems as well as an expressive end user oriented representation. Both are essential requirements since end users need other visualization techniques than experienced designers due to their different knowledge and interests.

Integrated Design and Simulation of Hybrid Systems

In this article we present a new approach for the design of hybrid systems composed of discrete and continuous parts. In our approach the system designers can start their specifications with the discrete as well as with the continuous parts. Both paradigms can be used with there own methodology and Tools. There are integration mechanisms for both paradigms. For the integrated simulation C code is generated. The advantages of our approach are demonstrated by modeling all important aspects of a system for building up motorcades. The model includes a discrete part selecting one of the different strategies modeled in the continuous parts. These are strategies for velocity and distance control for vehicles.

A generic system for interactive real-time animation

The authors present a new approach to an interactive design and analysis environment for visual languages. The main components, i.e., editor animator and interpreter are introduced. Their interactions are being investigated emphasizing the interpreter-animator interaction and defining an interface supporting different levels of automation. The interpreter performs the executions on a logical level and triggers the animator. The interactive animation provides a very high degree of liveness since it is based on the tight integration of the animator and editor. The proposed architecture permits the distributed implementation of a system for real-time animation. Their concepts are validated by the implementation of a debugging environment for the complete visual programming language Pictorial Janus.

Flat concurrent Prolog on transputers

Abstract Flat Concurrent Prolog (FCP) is a general purpose logic programming language designed for concurrent programming and parallel execution. Staring with a concise introduction of the language and its underlying computational model we describe how to implement a distributed FCP interpreter on a transputer environment using OCCAM. Basic techniques we used for exploiting and controlling parallelism are explained in terms of an abstract architecture. The result of mapping this abstract model on transputers is presented as concrete architecture. Substantial design issues are considered in detail.

Transforming SDL diagrams into a complete visual representation

We investigate a translation of SDL diagrams into the complete visual representation of Pictorial Janus (PJ) programs in order to analyze the specification by visual debugging and animation. We additionally introduce timing concepts to PJ (Timed PJ) for a mapping of the SDL timing statements. The concepts transforming SDL interaction and process diagrams into Timed PJ are outlined by an example sketching the transformation of an Ethernet CSMA/CD protocol specification.

Visual specification, modeling, and illustration of complex systems

This article introduces and discusses different innovative means for visual specification and animation of complex concurrent systems. It introduces the completely visual programming language Pictorial Janus (PJ) and its application in the customer-oriented design process. PJ implements a completely visual programming language with inherent animation facilities. The article outlines the transformation of purely visual PJ programs into textual imperative programming languages. The second part of the article investigates animated 3D-presentations and introduces a novel approach to an animated 3D programming language for interactive customer-oriented illustrations.

A visual programming language for qualitative data

Modeling of human knowledge and reasoning requires the formulation of uncertainty in its various forms. Fuzzy logic was introduced to directly support these applications (H. Zimmermann, 1991). Fuzzy control (FC) which is based on fuzzy logic allows one to control complex systems based on qualitative information like human knowledge (C. Geiger and G. Lehrenfeld, 1994). In fuzzy logic, fuzzy sets are usually defined and manipulated by means of complex mathematics, whereas the fuzzy control process is frequently outlined by visual sketches based on set diagrams in order to enhance the comprehension of the inference process. The rule based execution of this process usually follows the lines of rule based visual programming languages (VPLs), i.e., languages comparable to Agentsheets and ChemTrains. This strongly indicates that VPLs are thus well applicable for this use. We first outline the basic concepts of fuzzy logic and fuzzy control. Thereafter, we sketch a visual language which integrates fuzzy set diagrams in the visual representation of rules. The basic concepts are inherited from the complete visual programming language, Pictorial Janus (PJ). However, we significantly simplify PJs visual concepts in order to adapt it for our purpose.