The document is a complex object consisting of a document master, revision, and version. These are modeled as separate classes in the schema and are related by the SPFIncludesClass relationship. SmartPlant Foundation server and client functionality then treats this complex object as a single object in the client.
A complex object is always identified by the lowest class in this hierarchy, which in the case of a document is the document version. It is the document version that is retrieved, and the client consolidates the information from the parent revision and master.