The book presents an overview of the most fundamental aspects of the theory that underlies the Relational Database Model. It provides exact definitions of widely accepted concepts, and also covers some recent research topics, making the book very suitable in classes on database theory.

The Structure of the Relational Database Model

Object-oriented databases (OODBs) provide powerful data abstractions and modeling facilities, 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 requirements 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 uniform method of unnesting queries, regardless of their type of nesting.

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Optimizing object queries using an effective calculus

The authors describe how the characteristics of an object-oriented data model, such as object identity, complex object structure, methods, and class hierarchies, have an impact on the design of a query language. They also point out major differences with respect to relational query languages. The discussion is supported through the definition of OOPC, a formal object-oriented query language based on predicate calculus, which incorporates in a consistent formal notation most features of existing object-oriented query languages. >

Object-oriented query languages: the notion and the issues

SQL/NF: a query language for ¬ 1NF relational databases

Because of its small set of data types, the rela-tional model is constrained to simply structured data management tasks. For more advanced applications like engineering databases in the CAD/CAN area even a powerful extension like the NF' model is insufficient , yet: Important concepts like order and duplicates are not supported appropriately, and the free usage of composite items is prohibited by inherent asymmetries. These drawbacks can be removed by a data model which suooorts atomic data, lists, multisets, and tUpleS in"an orthogonal fashion. The necessary operations can be provided in an SQL-like framework. Compared with existing approaches, the expressive power could considerably be increased; nevertheless, the proposed SQL dialect has not become more complicated for comparable tasks, but more consistent and easier to understand.

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R Traunmueller

Papers

A database language for sets, lists and tables