SOAP messages with attachments - a definition
From an architecture and external specification viewpoint, SOAP Messages with Attachments is an extension to the SOAP 1.1 Recommendation from the World Wide Web Consortium (W3C).
The W3C SOAP messages with attachments document describes a standard way to associate a SOAP message with one or more attachments in their native format (for example GIF or JPEG) by using a multipart MIME structure for transport. This document defines specific use of the Multipart/Related MIME media type, and rules for the use of URI references to refer to entities bundled within the MIME package. It outlines a technique for a SOAP 1.1 message to be carried within a MIME multipart/related message in such a way that the SOAP processing rules for a standard SOAP message are not changed.
An associated W3C document Web Services Description Language (WSDL) outlines a technique for including bindings to MIME types in a WSDL file.
Passing SOAP messages with attachments through the Web services gateway
Writing the WSDL extensions for SOAP messages with attachments