Principles of Data Integration

2

Manipulating Query Expressions

The first step in answering a query posed to a data integration system is selecting which data sources are most relevant to the query. Making this decision relies on a set of methods for manipulating queries and reasoning about relationships between queries. This chapter covers such reasoning techniques in detail. While these techniques are very useful in data integration, they are also of independent interest and have been used in other contexts as well, such as query optimization and physical database design.

Section 2.1 begins with a review of database concepts that are used throughout the book. Section 2.2 describes techniques for query unfolding, where the goal is to reformulate a query, possibly posed over ...