FLORA: Implementing an Efficient DOOD System Using a Tabling Logic Engine ⋆ Guizhen Yang and Michael Kifer Department of Computer Science SUNY at Stony Brook Stony Brook, NY 11794, U.S.A. {guizyang, kifer}@CS.SunySB.EDU Abstract. This paper reports on the design and implementation of FLORA — a powerful DOOD system that incorporates the features of F-logic, HiLog, and Transaction Logic. FLORA is implemented by trans- lation into XSB, a tabling logic engine that is known for its efficiency and is the only known system that extends the power of Prolog with an equivalent of the Magic Sets style optimization, the well-founded seman- tics for negation, and many other important features. We discuss the features of XSB that help our effort as well as the areas where it falls short of what is needed. We then describe our solutions and optimization techniques that address these problems and make FLORA much more efficient than other known DOOD systems based on F-logic. 1 Introduction Deductive object-oriented databases (abbr. DOOD) attracted much attention in early 1990’s but difficulties in realizing these ideas and performance problems had dampened the initial enthusiasm. Nevertheless, the second half of the last decade witnessed several experimental systems [34, 20, 2, 24, 17, 27]. They, along with the proliferation of the Web and many recent developments, such as the RDF 1 standard, have fueled renewed interest in DOOD systems; in particular, systems for logic-based processing of object-oriented meta-data [15, 18, 28, 4, 5]. Also, a new field — processing of semistructured data — is emerging to address a specialized segment of the research on DOOD systems [1]. In this paper, we report our work on FLORA, a practical DOOD system that has already been successfully used to build a number of sophisticated Web- based information systems, as reported in [13, 19, 26]. By “practical” we mean a DOOD system that has high expressive power, is built on strong theoretical foundations and offers competitive performance and convenient software devel- opment environment. ⋆ Work supported in part by a grant from New York State through the program for Strategic Partnership for Industrial Resurgence, by XSB, Inc., through the NSF SBIR Award 9960485, and by NSF grant INT9809945. 1 http://www.w3.org/RDF/