Proposal for multi-reference support in MTOM

Here's a proposal for an extension to the current MTOM formulation to 
offer better support for multiple inclusion of the same data. The 
proposed extension  has the following properties:

- Preserves MTOM semantics of attachment inclusion in SOAP message 
infoset
- Supports existing 'Include' and 'Representation' semantics, use of 
extension is optional
- Supports multiple inclusion of attachments without replication of 
data in the serialized form
- Multiply included data replicated in message infoset, signatures over 
elements containing such data include attachment data rather than a 
reference to the data as woud be the case when using a Representation 
approach.


Infoset Form
============

This section shows via an example the infoset of a message after the 
binding has performed the MTOM deserialization (described later). XML 
1.0 is used as the most convenient syntax to express the infoset but 
this should be considered a purely abtract model of the message 
content.

<env:Envelope xmlns:env="..." xmlns:mtom="...">
   <env:Body>
     <app:Stuff xmlns:app="...">
       <app:Thing1 mtom:ContentID="someURI">
         some base64 text
       </app:Thing1>
       <app:Thing2 mtom:ContentID="someURI">
         some base64 text
       </app:Thing2>
       <app:Thing3>
         some base64 text
       </app:Thing3>
     </app:Stuff>
   </env:Body>
</env:Envelope>

Note that the same base64 data is included as the content of the Thing1 
and Thing2 EIIs, this is indicated by the value of the mtom:ContentID 
attribute being the same for both. Thing3 has no mtom:ContentID 
indicating that the optional multi-reference extension is not being 
used for the content of this EII.


Optimized (MIME) Wire Form
==========================

This section shows via an example the serialized form of a message 
using the MIME based MTOM.

Content-type: multipart/related; boundary="someBoundaryString"

--someBoundaryString
Content-Type: application/soap+xml

<env:Envelope xmlns:env="..." xmlns:mtom="...">
   <env:Body>
     <app:Stuff xmlns:app="...">
       <app:Thing1 mtom:ContentID="someURI">
         <mtom:Include href="someURI">
         <!-- depending on how mtom:ContentID is defined, the 
Include/@href may be redundant -->
       </app:Thing1>
       <app:Thing2 mtom:ContentID="someURI">
         <mtom:Include href="someURI">
       </app:Thing2>
       <app:Thing3>
         <mtom:Include href="someOtherURI">
       </app:Thing3>
     </app:Stuff>
   </env:Body>
</env:Envelope>

--someBoundaryString
Content-Type: image/png
Content-ID: someURI

binary picture data

--someBoundaryString
Content-Type: image/png
Content-ID: someOtherURI

binary picture data

--someBoundaryString--


Schema Types
============

<complexType name="OptimizationCandidate">
   <simpleContent>
     <extension base="xsd:base64Binary">
       <attribute name="ContentID" type="xsd:anyURI"/>
       <attribute name="MediaType" type="xsd:string"/>
       <!-- other attributes we define -->
     </extension>
   </simpleContent>
</complexType>

Terminology
===========

The following terminology is used in the description of the 
serialization and deserialization algorithms:

Optimization candidate:
   EII of type xsd:base64 or mtom:OptimizationCandidate.

Matching MIME part:
   MIME part whose content-id and/or content-location headers (TBD 
specify exact matching criteria) match an 
OptimizationCandidate/@ContentID.

Content:
   base64Binary child CIIs of an optimization candidate (excludes AII 
children)


Infoset to Wire Serialization
=============================

For each optimization candidate in the SOAP message
     - if no matching MIME part exists then create a matching MIME part 
from the optimization candidate's decoded content and AIIs
     - replace the content of the optimization candidate with a child 
mtom:Include EII


Wire to Infoset Deserialization
===============================

For each mtom:Include EII
     - replace the mtom:Include EII with base64 encoded attachment 
content

--
Marc Hadley <marc.hadley@sun.com>
Web Technologies and Standards, Sun Microsystems.