Chapter 11. XML in the Data Tier

Although XML is frequently a part of the data tier—because it stores data—this chapter concentrates on XML and databases. Databases, both relational and native XML, are part of many applications. You must, therefore, often store XML in those databases or retrieve some of the data in XML format. While the conversion of data to XML could be done in an intermediate layer of your application, it is sometimes more efficient to do this work within the database itself. This chapter will look at how you can store and retrieve XML from such common databases as Microsoft SQL Server and Oracle 10g. In addition, this chapter will cover XML databases, and their possible role in your applications.

XML and Databases

Although XML is an excellent format for moving data between platforms, applications, or application tiers, it may not be the best format to use for storing data for your application. As the volume of data increases, so too does the time it takes to search for and manipulate that data. Databases, on the other hand, minimize the query times, even for large data sets. Because of this, you might often combine XML and databases in some applications. This can create mismatches: Data types stored in the database may not be in the same format as XML, and the structure of the two are different. XML tends to be more loosely structured or hierarchical, and relational databases (the most common forms today) are designed around tabular data. Moving data in and out ...

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