SOAP, WSDL, and UDDI form the core foundation for the Web services architecture, but these technologies provide only the most basic functionality. As mentioned in Chapter 3, SOAP gives you a powerful extension mechanism via SOAP headers. You can use SOAP extensions to add advanced middleware functionality, such as security, management, and transactions, to the environment.
When extending SOAP, people can devise their own SOAP header structures and their own intermediaries to process them, but if you'd like to make your extra middleware services interoperable it's helpful to have standards for these SOAP extensions. Standard SOAP extensions ensure cross-vendor and cross-business interoperability.