XML — Using XML with Databases

Summary

The purpose of this tutorial was to introduce the concepts behind relational databases and explain how to integrate them with your XML applications. First, I provided a brief introduction to the theory behind relational databases, which is important to understand when you're mixing them with a different sort of data structure, like the one provided by XML. I then provided a very brief overview of SQL, which is the language used to query all relational databases. I then described the issues that arise when you're integrating relational databases with XML applications, and explained how using XML for data storage and XML as a document format differ. Finally, I demonstrated how to export XML data from an existing database, as well as how to perform a SQL query on a database and format the results as an XML document.

Q&A

Q.	Don't some databases provide features specifically for handling XML?
A.	Most major relational databases (like Oracle, Microsoft SQL Server, and IBM's DB2) support XML natively. The problem is that none of them support XML in the same way. If you use a database that provides XML support, you should look at the vendor documentation and decide whether you want to use it. The specific XML support in each of those databases is unfortunately beyond the scope of this lesson.
Q.	What about object-oriented databases? Aren't they better suited to use with XML?
A.	Object-oriented databases are more appropriate for storing XML data than relational databases, generally speaking. They're designed explicitly to handle the treelike data structures associated with object-oriented design. Treelike is also the best way to describe most XML data structures. However, object-oriented databases have not displaced relational databases on the market and are not standardized in the same manner as relational databases.

Workshop

The Workshop is designed to help you anticipate possible questions, review what you've learned, and begin learning how to put your knowledge into practice.

Quiz

1.	What SQL statement do you use to retrieve data from a database?
2.	What is the drawback to exporting a database table as an XML document, such as was done in this chapter using phpMyAdmin?
3.	Why is it a good idea to break down XML documents used for data storage into tables when storing the data in a relational database?

Quiz Answers

1.	The SQL statement used to retrieve data from a database is the `SELECT` statement.
2.	The drawback to exporting a database table as an XML document is that you typically have to do it manually, which isn't ideal for web applications that need to query a database for XML data dynamically. Furthermore, exporting an entire table is usually less useful than targeting data that matches a specific query.
3.	When you use XML documents for data storage, it's a good idea to convert them into tables when using a relational database so that you can take advantage of SQL when you're retrieving data from the database.

Exercises

1.	Set up your own MySQL database, and then modify the PHP example from this lesson to work with it.
2.	Try passing in different parameters to the PHP example to alter the SQL query, and therefore the resulting XML file.