Structured documents (e.g., SGML) can benefit a lot from database support and more specifically from object-oriented database (OODB) management systems. This paper describes a natural mapping from SGML documents into OODB's and a formal extension of two OODB query languages (one SQL-like and the other calculus) in order to deal with SGML document retrieval. Although motivated by structured documents, the extensions of query languages that we present are general and useful for a variety of other OODB applications. A key element is the introduction of paths as first class citizens. The new features allow to query data (and to some extent schema) without exact knowledge of the schema in a simple and homogeneous fashion. 1 Introduction Structured documents are central to a wide class of applications such as software engineering, libraries, technical documentation, etc. They are often stored in file systems and document access tools are somewhat limited. We believe that (object-oriented) d...

Abstract: We provide an overview of the Garlic project, a new project at the IBM Almaden Research Center. The goal of this project is to develop a system and associated tools for the management of large quantities of heterogeneous multimedia information. Garlic permits traditional and multimedia data to be

We show how structured data stored in files can benefit from standard database technology and in particular be queried and updated using database languages. We introduce the notion of structuring schema which consists of a grammar annotated with database programs and of a database schema. We study the translation from structured strings to databases, and the converse. We adapt optimization techniques from relational databases to our context. 1 Introduction Database systems are concerned with structured data. Unfortunately, data is often stored in an unstructured manner (e.g., in files) even when it does have a strong internal structure (e.g., electronic documents or programs) . In this paper, we consider how data stored as strings can benefit from standard database technology and in particular be queried and updated using database languages. In actual systems, data is often stored as string for obvious historical reasons. The problem that we are considering is thus very general. Tools...

We consider the problem of storing and accessing documents (SGML and HTML, in particular) using database technology. To specify the database image of documents, we use structuring schemas that consist in grammars annotated with database programs. To query documents, we introduce an extension of OQL, the ODMG standard query language for object databases. Our extension (named OQL-doc) allows to query documents without a precise knowledge of their structure using in particular generalized path expressions and pattern matching. This allows us to introduce in a declarative language (in the style of SQL or OQL), navigational and information retrieval styles of accessing data. Query processing in the context of documents and path expressions leads to challenging implementation issues. We extend an object algebra with new operators to deal with generalized path expressions. We then consider two essential complementary optimization techniques: 1. we show that almost standard database optim...

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.

Many declarative query languages for object-oriented databases allow nested subqueries. This paper contains the first (to our knowledge) proposal to optimize them. A two-phase approach is used to optimize nested queries in the object-oriented context. The first phase---called dependency-based optimization---transforms queries at the query language level in order to treat common subexpressions and independent subqueries more efficiently. The transformed queries are translated to nested algebraic expressions. These entail nested loop evaluation which may be very inefficient. Hence, the second phase unnests nested algebraic expressions to allow for more efficient evaluation. 1 Introduction Many declarative query languages for object-oriented database management systems have been proposed in the last few years (e.g. [3, 5, 2, 18, 14]). To express complex conditions, access nested structure, or produce nested results, an essential feature found in these languages is the nesting of q...

We define a standard of effectiveness for a database calculus relative to a query language. Effectiveness judges suitability to serve as a processing framework for the query language, and comprises aspects of coverage, manipulability and efficient evaluation. We present the monoid calculus, and argue its effectiveness for object-oriented query languages, exemplified by OQL of ODMG-93. The monoid calculus readily captures such features as multiple collection types, aggregations, arbitrary composition of type constructors and nested query expressions. We also show how to extend the monoid calculus to deal with vectors and arrays in more expressive ways than current query languages do, and illustrate how it can handle identity and updates. 1 Introduction A much-touted advantage of the relational data model is the existence of a formal calculus and algebra to model database queries. In practice, these formalisms fail to model many of the features present in commercial query languages (e.g...

Algebraic transformation and optimization tech-niques have been the method of choice in relational query execution, but applying them in OODBMS is difficult due to the complexity of object-oriented query languages. This paper demonstrates that the problem can be simplified by mapping an OO data model to the binary ralational model implemented by Monet, a state-of-the-art database kernel. We present a generic mapping scheme to flatten data models and study the case of a straightforward object-oriented model. We show how flattening enabled us to implement a query algebra, using only a very limited set of simple oper-ations. The required primitives and query execution strategies are discussed, and their performance is eval-uated on the 1GB TPC-D benchmark, showing that our divide-and-conquer approach yields excellent results. 1

Object-oriented databases (OODBs) provide powerful data abstractions and modeling facili-ties, but they generally lack a suitable framework for query processing and optimization. The development of an effective query optimizer is one of the key factors for OODB systems to successfully compete with relational systems, as well as to meet the performance require-ments of many nontraditional applications. We propose an effective framework with a solid theoretical basis for optimizing OODB query languages. Our calculus, called the monoid comprehension calculus, captures most features of ODMG OQL, and is a good basis for expressing various optimization algorithms concisely. This article concentrates on query unnesting (also known as query decorrelation), an optimization that, even though it improves performance considerably, is not treated properly (if at all) by most OODB systems. Our framework generalizes many unnesting techniques proposed recently in the literature, and is capable of removing any form of query nesting using a very simple and efficient algorithm. The simplicity of our method is due to the use of the monoid comprehension calculus as an intermediate form for OODB queries. The monoid comprehension calculus treats operations over multiple collection types, aggregates, and quantifiers in a similar way, resulting in a

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