众所周知BizTalk架构在Subscribe-Publish模型上，因此可以使用BTS实现可维护性，灵活性，可扩展性都很高的解决方案，翻到一篇文章解释这个模型的两大角色- Subscriber和Publisher，写的很详细，推荐给大家。
Publishers include receive ports that publish messages that arrive in their receive locations, orchestrations that publish messages when sending messages or starting another orchestration asynchronously, and solicit/response send ports that publish messages when they receive a response from the target application or transport.
In BizTalk Server, there are two main types of subscriptions: activation and instance. An activation subscription is one specifying that a message that fulfills the subscription should activate, or create, a new instance of the subscriber when it is received. Examples of things that create activation subscriptions include send ports with filters or send ports that are bound to orchestrations, and orchestration receive shapes that have their Activate property set to true. An instance subscription indicates that messages that fulfill the subscription should be routed to an already-running instance of the subscriber. Examples of things that create instance subscriptions are orchestrations with correlated receives and request/response-style receive ports waiting for a response from BizTalk Server.
Subscriptions are created by service classes in BizTalk Server
A subscription is a collection of comparison statements, known as predicates, involving message context properties and the values specific to the subscription. For example, Message Type is a context property of messages and many subscriptions specify the message type in their subscription.
When a send port is enlisted, the port creates, at a minimum, a subscription for any message with that send port’s transport ID in the context. This allows the send port to always receive messages intended specifically for it. When an orchestration port is bound to a particular send port, the information about that binding is stored in the BizTalk Management database. When messages are sent from the orchestration through the port bound to the physical send port, the Transport ID is included in the context so that the message gets routed to that send port. However, it is important to note that this send port is not the only send port that can receive messages sent from the orchestration. When an orchestration sends a message, that message is published to the MessageBox with all of the relevant promoted properties. The bound send port is guaranteed to receive a copy of the message because the transport ID is in the context, but any other send port, or orchestration, can have a subscription that also matches the message properties. It is very important to understand that any time a message is published directly to the MessageBox, all subscribers with matching subscriptions will receive a copy of the message.
原文地址：http://interviewquestions4u.com/microsoft/biztalk-server/explain-the-publisher-subscriber-of-biztalk.html