The DocumentSpec class in the Microsoft.BizTalk.Component.Interop namespace of the Microsoft.BizTalk.Pipelines assembly is commonly used in custom pipeline components (particularly assemblers in disassemblers) to represent a compiled BizTalk schema (a document specification).
This class has one interesting method: CreateXmlInstance(), which can generate an sample instance XML based on the associated schema [1]. Recently I saw a question in the BizTalkGurus forum about how to use this functionality if you had a schema definition with multiple potential root elements.
Turns out its pretty easy, once you understand how DocumentSpec works and how Schemas are compiled into BizTalk assemblies.
The constructor for the DocumentSpec class takes two arguments: The docSpecName (schema name) and the name of the assembly it is defined in.
The clue to support multi-root schemas is that the docSpecName is, in reality, the namespace + type name of the class generated by the compiler when you compile the Schema into the BizTalk assembly. Each schema becomes one class in the generated code.
If the schema has a single root, that's the end of it; All you need to know is that docSpecName == Namespace.ClassName. If the schema has multiple roots, however, each root becomes a nested class within the schema class.
The way to select which root element to use for the sample instance generation, then, is to provide the type name of the root element nested class as to the DocumentSpec constructor instead of the name of the schema class. In other words, in this case docSpecName == Namespace.SchemaClass+RootClass.
[1] One annoyance of this method is that it takes a TextWriter argument but doesn't actually write the generated XML into it; instead it returns a Stream you need to read!
