© 2009 Old City Publishing, Inc. Published by license under the OCP Science imprint, a member of the Old City Publishing Group Tech., Inst., Cognition and Learning, Vol. 4, pp. 125–149 Reprints available directly from the publisher Photocopying permitted by license only 125 TICL 2: Knowledge Representation, Associated Theories and Implications for Instructional Systems Dialog on Deep Structures AERA Tuesday, March 25, 2008 JOSEPH M. SCANDURA, KEN KOEDINGER, STELLAN OHLSSON, ANTONIJA MITRTOVIC AND GILBERT PARQUETTE INTRODUCTION This discussion forum is designed to compare and contrast major alternative deep infrastructures on which progress in TICL depends. This issue has the goal of increasing understanding, specifically by exposing and clarifying basic simi- larities and differences between three invited articles in TICL Vol. 5, No. 2. Each focuses on a different basic approach to deep infrastructure in TICL. The Ohlsson & Mitrovic article focuses on production systems (PS) and constraint based mod- eling (CBM), and their use in building ITS. Paquette focuses on instructional systems derived from instructional design principles and relational networks. Scandura focuses on Abstract Syntax Trees (ASTs) and the central role they play in Structural Learning Theory (SLT) and in building adaptive and configurable tutoring systems derived thereon. The ensuing discussion begins with a dialog involving the three sets of authors, and those they have directly challenged. In all cases the goal has been both clari- fication and comparison. Initially the dialog focuses on comments and responses about the three core articles, by authors themselves and/or those whose ideas they may have challenged. Once these authors have had their say, probing questions, insightful comments and reasoned criticisms based on or deriving from the arti- cles and ensuing discussion will be welcomed from informed researchers who have read the articles and the above commentary. Questioners will include both other authors in the special triple issue, and invited questioners at a forthcoming 2008 TICL symposium in New York. All are leaders in the field. 125-149 pp TICL_ Sandura COMMENTARY.indd 125 2/5/2009 5:42:56 PM