Multipart Messages in BizTalk Server 2006
Multipart messages allow for the grouping of multiple parts into a single message. All messages within BizTalk Server are multiple massages, although most of them just have a single part (the message body), and therefore are not created as a multipart message within orchestrations.
Within a BizTalk orchestration, you can easily build multipart messages containing one or more documents. A multipart message can only have one BODY but any number of other additional parts. As we know, BizTalk sets a message context property called BTS.MessageType. For multipart messages, BizTalk just adopts the BODY part as its message type (the BODY part schema’s target namespace + “#” + the root node name.)
You can get more features on Multipart message in BizTalk server from the articles as follows.
1. BizTalk Secrets: using Multi-Part Messages instead of directly using Schemas
http://home.infusionblogs.com/kguenther/Lists/Posts/Post.aspx?ID=1826
2. 提高 BizTalk 编程能力的 8 点技巧和窍门
http://msdn.microsoft.com/msdnmag/issues/07/05/BizTalk/default.aspx?loc=zh