This part of the book deals with the lowest layers of the Web services stack:

SOAP, discussed in Chapter 4, “SOAP,” is the lingua franca of Web services. It is the message format that used to send Web services messages. SOAP is an XML-based format offering a simple message envelope structure that allows powerful features (described later in this book) to be built on top of it.

WS-Addressing, discussed in Chapter 5, “Web Services Addressing,” gives SOAP a set of headers to route messages. The functionality that it offers is very much analogous to e-mail headers such as From, To, Subject, ReplyTo, and so on, incarnate as SOAP headers.