Chapter 7: XML in Heterogeneous Environments

Overview

From what you have seen of XML and different database engines so far, it should be clear that XML is not just data. The added benefit of XML is that it also provides structure for that data. Thus it contains metadata, which is data about the data. One of the reasons this book includes specifics for different database engines is to show some of the different ways that databases operate with XML. This includes databases such as Oracle and SQL Server.

The beauty of XML is that the data and general structure of XML documents is an established and widely accepted standard. XML is also very easy to use and understand. Therefore passing XML documents, which are just data with some structure, between different database engines and even different operating systems and hardware is easy. The easy part of this process tends to break down a little when trying to push data into and out of the various different databases. There are various ways to solve these problems. One solution is to use the tools available to the different database engines. Another solution is to try to apply standards not only to XML, but also to the different databases. Additionally, standards can even be applied to the ways in which XML is transferred between different computers.

Weve really only touched the surface of Oracle and SQL Server databases. For example, there are many other XML capabilities in Oracle Database. Additionally, numerous other database engines include XML capabilities for example, DB2 from IBM, MySQL, and others. There are even capabilities for managing XML documents in tools such as Microsoft Excel. The primary purpose of the previous two chapters was to present a very brief picture of what different database engines, and different software, can do independently when youre working with XML documents.

This chapter shows you how to transfer XML data between different platforms and databases, regardless of which specific database is used at either end point of an XML data transfer. One of the ideas behind the existence of XML is to allow for sharing of data, without regard for whatever is at either end of a transfer.

Appendix E covers more on different database engines and their XML capabilities.

In this chapter you learn about:

• Simple XML document transfer

• Sharing of XML documents using Web Services

• What a Web Service is

• What SOAP is

• Applying context semantics to XML documents using SOAP