Marc Hadley's Blog

July 2003 Archives

W3C XML Protocol WG Publishes SOAP MTOM Working Draft

The W3C XML Protocol Working Group has published the first working draft of a SOAP Message Transmission Optimization Mechanism or MTOM for short. This specification shows the direction in which the WG is headed to address the handling of attachments for SOAP 1.2 messages.

On the wire, a message and its attachments are encapsulated within a MIME multipart/related envelope with the SOAP message as the root part. MTOM provides a standard referencing mechanism (the xbinc:Include element) to allow references to attachments from within the SOAP envelope. So far so much like SOAP Messages with Attachments.

The key difference to what has gone before is the logical inclusion of attachment data within the SOAP message XML Infoset for the purposes of the SOAP processing model. The concept is that, on receipt of a message, the SOAP binding logically replaces any xbinc:Include elements with their base64 encoded representation such that the data can be operated on like any other data contained directly within the SOAP Envelope. This means that, e.g., if an attachment is referenced only from a SOAP header and that header is removed then the attachment would also be removed from the MIME package.

There still remains a lot of work to be done to round out the document and tackle the edge cases, but IMO the basic concept is sound.

W3C Announces Workshop on Binary Interchange of XML Information Item Sets

Use of XML as a format for exchange of information has its plusses and minuses. XML is self describing and lends itself to more loosely coupled information exchange but it is quite verbose and processing it can be resource intensive. As a result, the subject of a more compact/performant binary representation of XML has become a perma-thread in discussion fora such as xml_dev. In response to this interest, the W3C has announced a Workshop on Binary Interchange of XML Information Item Sets.

My interest in this area is primarily its application to improving the performance of web services. Sun presented a technical session and BOF at the recent JavaONE conference describing the results of our investigations in this area as part of an internal project called 'Fast Web Services'. Fast web services uses ASN.1 to encode SOAP messages and other data described in XML Schema or WSDL in a very compact form and this work will form the basis of our position paper for the workshop.

Hope to see you there !

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