XML Binary Optimized Packaging. XOP makes XML files smaller by extracting binary parts such as images, sending them as a separate package with the document, and providing a uniform resource identifier as a link that recipient systems can use to access the extracted material, explained Lafon.
Currently, images and other binary data in a standard XML document must be encoded in base64 to be processed with the rest of the file. Base64 encodes binary data as ASCII text. The process divides three bytes of the original data into four bytes of ASCII text, making the file one-third bigger.
Using XOP eliminates the need for larger files, as well as the time and effort necessary to conduct base64 conversions.
Message Transmission Optimization Mechanism. The W3C has incorporated XOP's method for representing binary data into the MTOM communications protocol. In essence, MTOM implements XOP for SOAP messages. MTOM uses MIME (multipurpose Internet mail extensions) multipart to package the message, after XOP processing, with the extracted binary parts, Lafon explained.
Resource Representation SOAP Header Block. RRSHB provides a way for an application receiving an XML message—from which binary parts have been extracted via XOP and packaged with the main file via MTOM—to retrieve the binary parts. In the message's SOAP header, RRSHB references where the binary parts are and how the application receiving the message should access them.