The problem of answering queries using views is to find efficient methods of answering a query using a set of previously defined materialized views over the database, rather than accessing the database relations. The problem has recently received significant attention because of its relevance to a wide variety of data management problems. In query optimization, finding a rewriting of a query using a set of materialized views can yield a more efficient query execution plan. To support the separation of the logical and physical views of data, a storage schema can be described using views over the logical schema. As a result, finding a query execution plan that accesses the storage amounts to solving the problem of answering queries using views. Finally, the problem arises in data integration systems, where data sources can be described as precomputed views over a mediated schema. This article surveys the state of the art on the problem of answering queries using views, and synthesizes the disparate works into a coherent framework. We describe the different applications of the problem, the algorithms proposed to solve it and the relevant theoretical results.

– main idea; file structure – algorithms: insertion/split – deletion – search: range, nn, spatial joins – performance analysis – variations (packed; hilbert;...) 15-721 Copyright: C. Faloutsos (2001) 2 Problem • Given a collection of geometric objects (points, lines, polygons,...) • organize them on disk, to answer spatial queries (range, nn, etc) 15-721 Copyright: C. Faloutsos (2001) 3 1 (Who cares?)

. Traditionally, integrity constraints in database systems are maintained either by rolling back any transaction that produces an inconsistent state or by disallowing or modifying operations that may produce an inconsistent state. An alternative approach is to provide automatic "repair " of inconsistent states using production rules. For each constraint, a production rule is used to detect constraint violation and to initiate database operations that restore consistency. We describe an SQL-based language for defining integrity constraints and a framework for translating these constraints into constraint-maintaining production rules. Some parts of the translation are automatic while other parts require user intervention. Based on the semantics of our set-oriented production rules language and under certain assumptions, we prove that at the end of each transaction the rules are guaranteed to produce a state satisfying all defined constraints. We apply our approach to a good-sized example...

Distributed data processing is fast becoming a reality. Businesses want to have it for many reasons, and they often must have it in order to stay competitive. While much of the infrastructure for distributed data processing is already in place (e.g., modern network technology), there are a number of issues which still make distributed data processing a complex undertaking: (1) distributed systems can become very large involving thousands of heterogeneous sites including PCs and mainframe server machines � (2) the state of a distributed system changes rapidly because the load of sites varies over time and new sites are added to the system� (3) legacy systems need to be integrated|such legacy systems usually have not been designed for distributed data processing and now need to interact with other (modern) systems in a distributed environment. This paper presents the state of the art of query processing for distributed database and information systems. The paper presents the \textbook " architecture for distributed query processing and a series of techniques that are particularly useful for distributed database systems. These techniques include special join techniques, techniques to exploit intra-query parallelism, techniques to reduce communication costs, and techniques to exploit caching and replication of data. Furthermore, the paper discusses di erent kinds of distributed systems such as client-server, middleware (multi-tier), and heterogeneous database systems and shows how query processing works in these systems. Categories and subject descriptors: E.5 [Data]:Files � H.2.4 [Database Management Systems]: distributed databases, query processing � H.2.5 [Heterogeneous Databases]: data translation General terms: algorithms � performance Additional key words and phrases: query optimization � query execution � client-server databases � middleware � multi-tier architectures � database application systems � wrappers� replication � caching � economic models for query processing � dissemination-based information systems 1

We propose incorporating a production rules facility into a relational database system. Such a facility allows definition of database operations that are automatically executed whenever certain conditions are met. In keeping with the set-oriented approach of relational data manipulation languages, our production rules are also set-oriented---they are triggered by sets of changes to the database and may perform sets of changes. The condition and action parts of our production rules may refer to the current state of the database as well as to the sets of changes triggering the rules. We define a syntax for production rule definition as an extension to SQL. A model of system behavior is used to give an exact semantics for production rule execution, taking into account externally-generated operations, selftriggering rules, and simultaneous triggering of multiple rules. 1 Introduction Recently, there has been considerable interest in integrating production rules systems and database manag...

There has been extensive work in query optimization since the early ‘70s. It is hard to capture the breadth and depth of this large body of work in a short article. Therefore, I have decided to focus primarily on the optimization of SQL queries in relational database systems and present my biased and incomplete view of this field. The goal of this article is not to be comprehensive, but rather to explain the foundations and present samplings of significant work in this area. I would like to apologize to the many contributors in this area whose work I have failed to explicitly acknowledge due to oversight or lack of space. I take the liberty of trading technical precision for ease of presentation. 2.

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

In the past few years, query languages featuring generalized path expressions have been proposed. These languages allow the interrogation of both data and structure. They are powerful and essential for a number of applications. However, until now, their evaluation has relied on a rather naive and inefficient algorithm. In this paper, we extend an object algebra with two new operators and present some interesting rewriting techniques for queries featuring generalized path expressions. We also show how a query optimizer can integrate the new techniques. 1 Introduction In the past few years there has been a growing interest in query languages featuring generalized path expressions (GPE) [BRG88, KKS92, CACS94, QRS + 95]. With these languages, one may issue queries on data without exact knowledge of its structure. A GPE queries data and structure at the same time. Although very useful for standard database applications, these languages are vital for new applications dedicated, for insta...

The problem of answering queries using views is to nd ecient methods of answering a query using a set of previously materialized views over the database, rather than accessing the database relations. The problem has recently received signicant attention because of its relevance to a wide variety of data management problems. In query optimization, nding a rewriting of a query using a set of materialized views can yield a more ecient query execution plan. To support the separation of the logical and physical views of data, a storage schema can be described using views over the logical schema. As a result, nding a query execution plan that accesses the storage amounts to solving the problem of answering queries using views. Finally, the problem arises in data integration systems, where data sources can be described as precomputed views. This article surveys the state of the art on the problem of answering queries using views, and synthesizes the disparate works into a coherent framework. We describe the dierent applications of the problem, the algorithms proposed to solve it and the relevant theoretical results.

: An important issue for federated systems of diverse data sources is how to optimize cross-source queries, without building knowledge of individual sources into the optimizer. Garlic is a federated system with an emphasis on extensibility and diverse sources. To achieve these goals, data sources are attached to Garlic by means of a wrapper. Wrappers participate in query planning, telling Garlic what parts of a query a data source can do and how much it will cost. This paper describes a framework through which wrappers provide the necessary cost and cardinality information for optimization, and the facilities Garlic provides to make this task easier. Our framework makes it easy for wrappers to provide cost information, requires few changes to a conventional bottomup optimizer and is easily extensible to a broad range of sources. We believe that our framework for costing is the first to allow accurate cost estimates for diverse sources within the context of a traditional cost-based opti...