The goal of this work is to integrate in a general framework the different query optimization techniques that have been proposed in the object-oriented context. As a first step, we focus essentially on the logical aspect of query optimization. In this paper, we propose a formalism (i) that unifies different rewriting formalisms, (ii) that allows easy and exhaustive factorization of duplicated subqueries, and (iii) that supports heuristics in order to reduce the optimization rewriting phase. 1 Introduction Many declarative query languages for object-oriented database management systems have been proposed in the last few years (e.g. [4, 5, 9]). Currently, a very serious concern is their optimization. Interesting techniques have been imported from other environments or developed for this context. However, although complementary, these techniques are often supported by distinct formalisms. The implementation of a query optimizer is thus still an awkward and delicate operation. Clearly, i...

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

The explosion in complex multi-media content makes it crucial for database systems to support such data efficiently. We make the case that the next generation of object-relational database Data Type (E-ADT) technology, rather than on the “blackbox ” ADTs used in current systems. An E-ADT is an abstract data type that exposes the semantics of its methods. Query optimizations are performed using these semantics, resulting in efficient query processing. The added functionality does not compromise the modularity of data types and the extensibility of the type system. Fundamental architectural changes are required to build such a database system; these have been explored through the implementation of E-ADTs in Predutor. Initial performance results demonstrate an order of magnitude in performance improvements. 1

We describe the TIGUKAT objectbase management system that is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, functions as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this paper is on the object model, its implementation, the persistence model and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system and transaction manager.

In this paper we address the problem of controlling the execution of a query optimizer. We describe a control for the optimization process that is based on planning. The controller described here is a goal-directed planner that intermingles planning with the execution of query transformations, and uses execution results to direct further planning of optimizer processing. We describe this control in the context of the Epoq extensible architecture. Epoq is an approach to extensible query optimization that integrates specialized rewrite strategies through its extensible control mechanism. This paper describes our planning-based approach to extensible control and illustrates it with a simple example. 1 Introduction Optimization of a query is inherently a process of searching the space of expressions equivalent to the query. Typically, a given optimizer can only visit some portion of this space, since the set of transformation rules is usually incomplete, the cost of optimization must be ...

In this work, we propose and assess a technique called bypass processing for optimizing the evaluation of disjunctive queries with expensive predicates. The technique is particularly useful for optimizing selection predicates that contain terms whose evaluation costs vary tremendously; e.g., the evaluation of a nested subquery or the invocation of a user-defined function in an object-oriented or extended relational model may be orders of magnitude more expensive than an attribute access (and comparison). The idea of bypass processing consists of avoiding the evaluation of such expensive terms whenever the outcome of the entire selection predicate can already be induced by testing other, less expensive terms. In order to validate the viability of bypass evaluation, we extend a previously developed optimizer architecture and incorporate three alternative optimization algorithms for generating bypass processing plans. 1 Introduction During the past few years we have witnessed tremendous...

Adopting the blackboard architecture from the area of Artificial Intelligence, a novel kind of optimizer enabling two desirable ideas will be proposed. Firstly, using such a well-structured approach backpropagation of the optimized queries allows an evolutionary improvement of (crucial) parts of the optimizer. Secondly, the A 3 search strategy can be applied to harmonize two contrary properties: Alternatives are generated whenever necessary, and straight-forward optimizing is performed whenever possible, however. The generic framework for realizing a blackboard optimizer is proposed first. Then, in order to demonstrate the viability of the new approach, a simple example optimizer is presented. It can be viewed as an incarnation of the generic framework. 1 Introduction Query optimizers---no matter whether relational or object-oriented---are among the most complex software systems that have been built. Therefore, it is not surprising that the design of query optimizers is still a "hot...

Paper Number 323 In this paper we describe the design and implementation of OPT++, a tool for Extensible Database Query Optimization that uses an object-oriented design to simplify the task of implementing, extending, and modifying an optimizer. Building an optimizer using OPT++ makes it easy to extend the query algebra (to add new query algebra operators and physical implementation algorithms to the system), easy to change the search space explored, and also easy to change the search strategy used. Furthermore, OPT++ comes equipped with a number of search strategies that are available for use by an Optimizer{ Implementor. OPT++ considerably simpli es both, the task of implementing an optimizer for a new database system, and the task of experimenting with various optimization techniques and strategies to decide what techniques are best suited for that database system. We present the results of performance studies which validate our design and show that, in spite of its exibility, OPT++ can be used to build e cient optimizers. 1

In this thesis we address the problem of providing efficient processing of queries in the extensible environment induced by object-oriented databases. We define a framework for query processing in an object-oriented database and develop designs for major components of this framework. The framework encompasses an object-oriented data model, an algebra to query over that model, transformation rules for the algebra, an internal representation for queries expressed in the algebra, a cost model for analyzing query expressions, and an architecture for an extensible query optimizer. The major contributions of this thesis are an algebra and transformation rules, a representation, and an architecture for extensible query optimization. We show how these components fit into the framework and interact with each other. The EQUAL query algebra presented in this thesis is the first query algebra for object-oriented database systems to be completely consistent with data abstraction, and one of the few...

Query optimizers for persistent object systems should be extensible to react to user-supplied abstract types. Current architectures support only a single, non-extensible technique for controlling the optimization process. We propose an alternative to the current extensible architectures that will support multiple optimizer control strategies and the addition of new control strategies. The optimizer consists of a collection of optimization regions, each of which can transform queries according to a particular control strategy, set of transformations and cost model. A global optimizer control coordinates the movement of a query between these regions. This architecture provides extensibility in the optimizer's repertoire of control strategies through the addition of new regions. In this paper we describe our approach and demonstrate its utility by following the optimizer as it works on an example query. The optimizer will move the query between three distinct regions. The different region...