XQuery for Data Integration Many servlets do nothing more than integrate data from one or more sources to create an XML orHTML result. XML plays a central role in most data-intensive Web applications, and XQuery wasdesigned to make it easy to find data in XML input, process and transform XML, and create any desiredXML structure. XQuery simplifies programming with XML in the same way that SQL simplifiesprogramming with relational data and Java simplifies programming with objects — each languagewas designed for working with data using a particular data model, and supports the operations that arecommonly needed in the given paradigm.

In addition, the XQuery language was also designed to simplify data integration. Many Web applicationsneed to combine data from various sources, including XML, relational databases, legacy formats, andWeb Services. Each of these data sources typically has its own API and data model, and sometimesalso has its own query language. After finding the data it needs in each of these data sources, morecode is written to combine the data. Consider a servlet that combines data from two databases and aWeb Service — in the Java world, this typically involves coding to three different APIs, then writingJava code or JSP to combine the results, as illustrated below.