One of the basic functionalities of database management systems (DBMSs) is to be able to process declarative user queries. The first generation of object-oriented DBMSs did not provide declarative query capabilities. However, the last decade has seen significant research in defining query models (including calculi, algebra and user languages) and in techniques for processing and optimizing them. Many of the current commercial systems provide at least rudimentary query capabilities. In this chapter we discuss the techniques that have been developed for processing object-oriented queries. Our particular emphasis is on extensible query processing architectures and techniques. The other chapters in this book on query languages and optimization techniques complement this chapter. 1

1 Introduction This paper describes the design and implementation of an OODBMS, namely the METU Object-Oriented DBMS (MOOD). MOOD [Dog 94b] is developed on the Exodus Storage Manager (ESM) [ESM 92] and therefore some of the kernel functions like storage management, concurrency control, backup and recovery of data were readily available through ESM. In addition ESM has a client-server architecture and each MOOD process is a client application in ESM. The kernel functions provided by MOOD are the optimization and interpretation of SQL statements, dynamic linking of functions, and catalog management. SQL statements are interpreted whereas functions (which have been previously compiled with C ) within SQL statements are dynamically linked and executed. A query optimizer is implemented by using the Volcano Query Optimizer Generator. A graphical user interface, namely MoodView [Arp 93a, Arp 93b], is developed using Motif. MoodView displays both the schema information and the query results ...

. This paper describes the design and implementation of a kernel for an OODBMS, namely the METU Object-Oriented DBMS (MOOD). MOOD is developed on the Exodus Storage Manager (ESM). MOOD kernel provides the optimization and interpretation of SQL statements, dynamic linking of functions, and catalog management. SQL statements are interpreted whereas functions (which have been previously compiled with C++) within SQL statements are dynamically linked and executed. Thus the interpretation of functions are avoided increasing the efficiency of the system. A query optimizer is implemented by using the Volcano Query Optimizer Generator. A graphical user interface, namely MoodView, is developed using Motif. MoodView displays both the schema information and the query results graphically. Additionally it is possible to update the database schema and to traverse the references in query results graphically. Keywords: OODBMS kernel implementation, query optimization in OODBMSs, dynamic function link...

Rule--based query optimizers are recognized as particularly valuable for extensible and object--oriented database management systems by providing a high flexibility in adapting query optimization strategies to nonstandard application needs. On the other hand rule--based optimizers areproblematic with regard to run--time behavior for more complex queries as the generation of query plans based on a declarative rule base tends to be difficult to control. In this paper we show that this is not a fundamental problem of rule--based optimizers, but rather a question of careful design of the rule system. We exemplify this for one fundamental optimization problem, namely join enumeration for linear queries.There,arule--basedoptimizationstrategycanachievethetheoreticallyoptimalcomplexity. The design principles used to achieve this have been derived from and are used in the design of the VODAK query optimizer developed at GMD--IPSI.