It's easy to confuse BizTalk Messages with two different but closely related concepts: BizTalk Documents and Business Documents.
The BizTalk Message is the outer envelope in a BizTalk interchange. A BizTalk Message encloses one BizTalk Document, which encloses one or more inline Business Documents. The bulk of the process-relevant header information is contained in the BizTalk Document. The bulk of the application-relevant content is contained in the Business Document. You will have to master this message structure and grasp its details as second-nature in order to navigate the complexities of BizTalk application development and deployment.
Every BizTalk interchange consists of overlapping dialogues among three sets of e-commerce entities: BizTalk servers, BizTalk application-adapters, and line-of-business applications. The headers of the three nested objects (BizTalk Messages, BizTalk Documents, and Business Documents) contain information that helps these entities to collectively route, validate, process, and handle the content within Business Documents. The content of the three overlapping dialogues is as follows:
A BizTalk Message is what one BizTalk server exchanges with other BizTalk servers.
A BizTalk Document is what one BizTalk application-adapter exchanges with other BizTalk application-adapters.
A Business Document is what one line-of-business application exchanges with other line-of-business applications.
A BizTalk Message may also enclose one or more Attachments associated with the BizTalk Document, which are referenced in that document's "manifest." However, these Attachments often contain binary data files, and are transmitted outside the BizTalk Document. One technique for transmitting Attachments is as separate MIME body parts of the BizTalk Message. This approach is necessary due to the fact that XML documents cannot contain non-text content.
The BizTalk Message's outer envelope will vary in structure, according to the transport protocol used to transmit it. Unlike the BizTalk Document, which Microsoft has mapped out in fine detail, the structural details of the BizTalk Message's outer envelope are as yet undefined. However, it's clear that Microsoft is focusing on defining the BizTalk Message as a MIME body part for transmission over the leading Internet application-layer protocols: HyperText Transfer Protocol (HTTP), Simple Mail Transfer Protocol (SMTP), and File Transfer Protocol (FTP). In addition, Microsoft is defining the BizTalk Message envelope for transmission over message-oriented middleware protocols, such as its own proprietary Microsoft Message Queue (MSMQ) service. The vendor has promised to publish transport-specific BizTalk Message implementation guides in a separate document.