A Visualization Algorithm for Defeasible Logic Rule Bases over RDF Data Efstratios Kontopoulos 1 , Nick Bassiliades 1 , Grigoris Antoniou 2 1 Department of Informatics Aristotle University of Thessaloniki GR-54124 Thessaloniki, Greece {skontopo,nbassili}@csd.auth.gr 2 Institute of Computer Science, FO.R.T.H. P.O. Box 1385, GR-71110, Heraklion, Greece antoniou@ics.forth.gr Abstract. This work presents a visualization algorithm for defeasible logic rule bases as well as a software tool that applies this algorithm, according to which, a directed graph is produced that represents the rule base. The graph features distinct node types for rules and atomic formulas and distinct connection types for the various rule types of defeasible logic. 1. Introduction Logic and proofs posses a key role in the acceptance of the Semantic Web on behalf of the users. Defeasible reasoning [3] represents a rule-based approach to reasoning with incomplete, changing and conflicting information. Nevertheless, it is based on solid mathematical formulations and is, thus, not fully comprehensible by users, who often need graphical trace and explanation mechanisms for the derived conclusions. This paper presents a visualization algorithm for defeasible logic rule bases and a software tool that applies this algorithm. For the representation of the rule base, di- rected graphs are applied that feature distinct node and connection types. The tool is called dl-RuleViz and is implemented as part of VDR-DEVICE [1], an environment for modeling and deploying defeasible logic rule bases on top of RDF ontologies. 2. Visualizing a Defeasible Logic Rule Base The full theoretical approach, regarding the graphical representation of defeasible rea- soning elements was discussed in a previous work of ours [2]. For every class in the rule base, a class box with the same name is constructed. Class boxes are containers, which are dynamically populated with one or more class patterns. Class patterns ex- press conditions on filtered subsets of instances of the specific class and are populated with one or more slot patterns. Slot patterns represent conditions on slots (or class properties) and they consist of a slot name and, optionally, a variable and a list of value constraints. The variable is used for unifying the slot value, with the latter hav- ing to satisfy the list of constraints.