Visual exploration and retrieval of XML document collections with the generic system X2

This article reports on the XML retrieval system X2 which has been developed at the University of Munich over the last five years. In a typical session with X2, the user first browses a structural summary of the XML database in order to select interesting elements and keywords occurring in documents. Using this intermediate result, queries combining structure and textual references are composed semiautomatically. After query evaluation, the full set of answers is presented in a visual and structured way. X2 largely exploits the structure found in documents, queries and answers to enable new interactive visualization and exploration techniques that support mixed IR and database-oriented querying, thus bridging the gap between these three views on the data to be retrieved. Another salient characteristic of X2 which distinguishes it from other visual query systems for XML is that it supports various degrees of detailedness in the presentation of answers, as well as techniques for dynamically reordering and grouping retrieved elements once the complete answer set has been computed

Isabelle/PIDE as Platform for Educational Tools

The Isabelle/PIDE platform addresses the question whether proof assistants of the LCF family are suitable as technological basis for educational tools. The traditionally strong logical foundations of systems like HOL, Coq, or Isabelle have so far been counter-balanced by somewhat inaccessible interaction via the TTY (or minor variations like the well-known Proof General / Emacs interface). Thus the fundamental question of math education tools with fully-formal background theories has often been answered negatively due to accidental weaknesses of existing proof engines. The idea of "PIDE" (which means "Prover IDE") is to integrate existing provers like Isabelle into a larger environment, that facilitates access by end-users and other tools. We use Scala to expose the proof engine in ML to the JVM world, where many user-interfaces, editor frameworks, and educational tools already exist. This shall ultimately lead to combined mathematical assistants, where the logical engine is in the background, without obstructing the view on applications of formal methods, formalized mathematics, and math education in particular.Comment: In Proceedings THedu'11, arXiv:1202.453

Constructing program animations using a pattern-based approach

The aim of this paper is to discuss how our pattern-based strategy for the visualization of data and control flow can effectively be used to animate the program and exhibit its behavior. That result allows us to propose its use for Program Comprehension. The animator uses well known compiler techniques to inspect the source code in order to extract the necessary information to visualize it and understand program execution. We convert the source program into an internal decorated (or attributed) abstract syntax tree and then we visualize the structure by traversing it, and applying visualization rules at each node according to a pre-defined rule-base. In order to calculate the next step in the program execution, a set of rewriting rules are applied to the tree. The visualization of this new tree is shown and the program animation is constructed using an iterative process. No changes are made in the source code, and the execution is simulated step by step. Several examples of visualization are shown to illustrate the approach and support our idea of applying it in the context of a Program Comprehension environment.FC