Overview

BizTalk Server is a great tool that can aid in the development in integration and SOA solutions. It is a force multiplier that allows one developer to perform the work of many. It is reliable and scalable. It is also a little difficult to get your head around at first. One of the greatest difficulties developers have starting out with BizTalk is to understand how types work in BizTalk Server. This is a pretty straightforward concept in .NET so the answer can throw off some people.

Types of Types

BizTalk primarily has two major types of types: Message Types and .NET Types. Everything in BizTalk is one of these and some things are both. The .NET types are simple enough, but we'll discuss some of their implications shortly. The Message Types are less so. Being a Messaging Platform everything that flows into or out of BizTalk Server is a message. Binary, XML, Text they are all messages. BizTalk identifies XML Message Types based on the namespace and root node of the XML instance itself. Since XML legally only allows one root node in a document this is a pretty standard identification. An example would be "http://novaenterprisesystems.com/schemas/sql#SqlRequest" where "SqlRequest" is the root element of the message and the schema is "http://novaenterprisesystems.com/schemas/sql". This works fine for XML messages, but other messages don't really work the same.

Types in Contexts

All messages in BizTalk's Messaging Engine are represented as an instance of Microsoft.BizTalk.Message.Interop.IBaseMessage and in a Pipeline the same holds true (as Pipelines are messaging components). Once in an Orchestration a message is represented as an instance of Microsoft.XLANGs.BaseTypes.XLANGMessage and can be sent to or from a user component as such. Interestingly enough these types cannot be converted between them so you'll generally use IBaseMessage in Pipeline Components and XLANGMessage exclusively in Orchestrations.

To make things a little more complicated any message in an Orchestration it is implicitly understood to be an instance of System.Xml.XmlDocument. It is not so much that these classes are all related, but they are functionally and have both practical and historic reasons for this arrangement. One is that it allows you a simple way to deal with non XML messages in orchestrations, you can specify their type as XmlDocument and handle just about any type of message, even binary. That said if you have a binary message and try to use any of the members of XmlDocument on it you will receive an exception from the Orchestration Engine.

These different interfaces allow different types of interactions with messages in their own contexts' which can sometimes be challenging until you understand the lay of the land so to speak.

To sum it up in these contexts messages are these types:

Messaging Engine: IBaseMessage

Orchestration: XLANGMessage or XmlDocument

Later I will post on how to create messages in the different parts of BizTalk Server.