Beginning XML, 5th Edition

Chapter 10

XML and Databases

WHAT YOU WILL LEARN IN THIS CHAPTER:

• Why databases need to handle XML
• The differences between relational and native XML databases
• What basic XML features are needed from a database
• How to use the XML features in MySQL
• How to use the XML features in SQL Server
• How to use features in eXist

Not very along ago, you had two main options when deciding where to store your data. You could go for the traditional solution, a relational database such as Oracle, Microsoft’s SQL Server, or the ever-popular open source MySQL. Alternatively, you could choose to use XML. A relational database has the advantage of efficiently storing data that can be expressed in a tabular form, although performance can be a problem if you need to join many tables together. XML has the advantage of coping with nested data or documents that can’t be easily broken down further. After a while, it became apparent that a hybrid of the two was needed: a system that could store tabular data alongside XML documents, giving the user the ability to query and modify the XML as well as perform standard operations against the relational data. This would create an all-purpose storage center giving the best of both worlds.

UNDERSTANDING WHY DATABASES NEED TO HANDLE XML

Relational databases grew from the work of Edgar Codd in the 1970s. He was the first to provide a solid mathematical foundation for the main concepts found in these systems, such as tables (which he called relations), primary keys, ...