XML Indexes

Abstract

The past couple chapters focused on indexing what is commonly referred to as structured data, where there is a common schema and organization around the data and its storage. In this chapter, the indexing focus shifts to unstructured and semistructured data. With both structured and unstructured data, the task of indexing is to gain optimal efficiency for retrieving and manipulating data, but the data types that represent these types of data have differences in how they are stored in the database. These differences dictate how and why indexing is implemented as well as how the indexes are used by the query optimizer. SQL Server has a specialized data type for storing the most common type of unstructured and semistructured data, XML. This chapter explores the types of indexes offered by SQL Server for dealing with XML data. The chapter will also show the impact of those indexes on the types of queries that can be written against XML data using XQuery and the impact on the choices made by the optimizer.