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Meta programming is the act of reasoning about a computational system. For example, a program in Prolog can reason about a program written in Smalltalk. Reflection is a more powerful form of meta programming where the same language is used to reason about, and act upon, itself in a causally connected way. Thus on the one hand we have meta programming that allows different languages or paradigms to be used, but without causal connection, while on the other hand we have reflection that offers causal connection but only for a single language. This paper combines both and presents inter-language reflection that allows one language to reason about and change in a causally connected way another language and vice versa. The fundamental aspects of inter-language reflection and the language symbiosis used therein, are discussed. Moreover the implementation of two symbiotic reflective languages is discussed: Agora/Java and SOUL/Smalltalk.

System and Software Engineering LabVrije Universiteit Brussel Maja.D'Hondt @vub.ac.be Viviane Jonckers System and Software Engineering LabVrije Universiteit Brussel Viviane.Jonckers@vub.ac.be ABSTRACT Software applications often consist of implicit knowledge for making decisions or giving advice in addition to objectoriented functionality. A rule-based system can be employed for representing and reasoning with this knowledge. Although several hybrid systems exist that combine objectoriented programming and rule-based reasoning, a survey we conducted reveals that both paradigms are not well integrated and programs are tightly coupled.We propose hybrid aspects for integrating object-oriented programming and rule-based reasoning. As expected, hybrid aspects specify join points where normal execution is interrupted and advice is executed. However, since two different languages are involved, we need join point models for both and advice that activates both. As such, we complement a simple join point model for object-oriented programming with a join point model for rule-based reasoning. Hybrid advice is independent of the interrupted language and sup-ports sending messages as well as activating rules. It uses values of either language transparently.We present OReA, an implementation of hybrid aspects for weaving Smalltalk and a rule-based system. We discuss and illustrate two applications of hybrid aspects.

Software applications often contain implicit knowledge in addition to functionality which is inherently object-oriented. Many approaches and systems exist that focus on separating rule-based knowledge from object-oriented functionality and representing it explicitly in a logic reasoning system. Support for seamless integration of this knowledge with the object-oriented functionality improves software development and evolution. Our hypothesis is that a linguistic symbiosis is required between the logic reasoning and object-oriented programming paradigms in order to achieve seamless integration.This paper presents a symbiotic extension of SOUL, a system which implements a logic programming language and a production system in Smalltalk. The presence of these two logic reasoning systems in SOUL ensures a comprehensive coverage of rule-based reasoning styles, more specifically forward and backward chaining. Our approach is evaluated by means of two case studies. We summarise a comprehensive survey, which shows that existing systems do not fully support seamless integration.