Semantics of behavioral inheritance in deductive object-oriented databases

Semantics of Behavioral Inheritance in Deductive Object-Oriented Databases Hasan M. Jamil, Ph.D. Concordia University, 1996 We argue that powerful models for supporting next generation database and knowledgebase applications can be built by extending semantic data models in the direction of Object Oriented modeling. It is clear that modeling such new applications will require concepts like modularity, behavioral abstraction, derived schema components, and database knowledge (e.g. constraints). Most of the required concepts are already present in these two seemingly parallel models in the form of the notions like object identity, inheritance, encapsulation, methods, virtual objects and classes. but have important di erences. We present a conceptual Abstract Data Model called the Object Relationship (OR) model which reconciles semantic and object-oriented data models and extends the modeling capability with additional concepts like withdrawal, strati ed constraints, methods in relationships, and encapsulation. We then propose a novel semantics for object-oriented deductive databases as a formalization of the ORmodel in the direction of F-logic to logically account for behavioral inheritance, con ict resolution in multiple inheritance hierarchies, and overriding. We introduce the ideas of withdrawal, locality, and inheritability of properties (i.e., methods and signatures). Exploiting these ideas, we develop a declarative semantics of behavioral inheritance and overriding without having to resort to non-monotonic reasoning. Con ict resolution in our framework can be achieved both via speci cation and by detection. The possibility of speci cation based con ict resolution through withdrawal allows users to state inheritance preference. We present a formal account of the semantics of our language by de ning a model theory, proof theory and a xpoint theory. We also prove that the di erent characterizations of our language are equivalent. iii We nally present an elegant technique to reduce inheritance to deduction based on the idea of constrained deduction, called the i-completion. The reduction technique makes it possible to implement object-oriented databases with inheritance, overriding and con ict resolution in a purely deductive system. An ORLog prototype implementation on Coral deductive database system is discussed based on this reduction technique. We are able to exploit the rich set of query optimization techniques available in Coral since the implementation does not require meta-interpretation. iv Dedication To My Parents and To My Grandfather Abdul Hai Acknowledgments I have been fortunate to have Dr. Laks V. S. Lakshmanan and Dr. Fereidoon Sadri as my thesis supervisors. They always encouraged me to pursue the best and strive for excellence. I was introduced to the challenging eld of logic and object-orientation by Dr. Lakshmanan and he gave me the foundation I needed to advance in my research. Despite a busy schedule, he always had the time for me, and his guidance and our numerous discussions paved the way for the completion of this thesis. I thank him for taking the time to read the manuscript of this thesis and xing several bugs. I would like to express my indebtedness to him for his exceptional guidance and inspiration. Fereidoon gave me the basics of databases and rudimentary details of deductive databases at the early stage of my research. The interest he developed in me later triggered my fascination in deductive object-oriented databases. He then introduced me to uncertainty management in databases, and always encouraged me to explore new frontiers in research. It was a real delight doing research with him in these areas. He always had faith in me, took interest in me and helped me in shaping my professional life. I am grateful to him for everything he did for me. I was also blessed by two great souls, Dr. V. S. Alagar and Dr. Peter Grogono, during my stay at Concordia. They always gave me the much needed encouragement, and helped me change my views towards teaching, research and life as a whole. I received so much appreciation from them that I remain ever thankful. I am glad that I came to know Michele Bugliesi from the University of Padova, Italy. We shared interesting ideas and worked as colleagues. I had an exciting and enlightening time working with him and doing insightful research. He presented to me an entirely new dimension of logical systems and helped me develop a deeper understanding of logic programming as a whole. This was instrumental in shaping the research contained in this thesis. I owe to him all that I learned from him and I am thankful that we are friends. vi Thanks are also due to Michael Kifer (State University of New York, USA), Rodney Topor (Gri th University, Australia), Kenneth Smith (University of Illinois at Urbana-Champaign, USA), Laura Giordano (University of Torino, Italy), and Paul Johannesson (Stockholm University, Sweden) for the many interesting discussions we have had from time to time. My rst year of study in Concordia was made easy by Rajwant Kohli. He took the time to upgrade me to Unix itro , and explained to me every necessary details I needed to know to survive in a new environment. Ramesh Achuthan, Basudeb Das, Khaled Jababo, Alexander Lakher, Nematollah Shiri, and Iyer Subramanian have been excellent friends. I thank them all for being extremely helpful in so many ways. I thank my dearest friend Mahbubur Rahman for helping me during the worst times of my life in Montreal. I would like to express my sincere gratitude to the analyst pool of the Computer Science Department and the department secretaries Edwina Bowen, Terry Czernienko, Halina Monkiewicz and Stephanie Roberts for being so helpful and cooperative. Special thanks are due to Stan Swiercz for helping me with Unix, Coral, and WWW. Thanks are also due to Ianina Orenman for working with me for the implementation of ORLog, for which she did an excellent job. My graduate study at Concordia has been supported by several grants which I would like to gratefully acknowledge. I received nancial support from the Canadian Commonwealth Scholarship and Fellowship Plan and from the University of Dhaka, Bangladesh for my entire graduate study at Concordia. I also received stipends for one year and partial support for conference travel from NSERC (Canada) and FCAR (Quebec). Finally, I would like to thank my family { my wife Nusrat, my daughter Nishat, my parents and my brothers (specially my brother Hasan Zaman) for allowing me all the time I needed to complete this thesis, for forgiving me for not being able to be there when they needed me most, and for supporting me during my thesis work in every way they could { a debt which I will never be able to repay. vii