Design Documentation
The Design Document shall be an extension of Requirements Analysis Design.
"The Design Document will comprise a revised and much more detailed description of Object Model" in both textual form (class descriptions) and graphical form (object model diagrams). You could use additional notation to show the implementation decisions, such as arrows showing traversal direction of associations and pointers from attributes to another objects.
The Functional Model could also be extended during design phase and it must be kept current. It is a seamless process since object design uses same notation as analysis, but with more specifics and detail. It is good idea to state all operation interfaces by giving their arguments, input-output mappings, results, and side effects.
Despite seamless conversion from analysis to design, it is probably a good idea to keep Design Document distinct from Analysis Document. Since the shift in viewpoint from an external user's view to internal implementer's view, design document includes many optimizations and implementation artefacts. It is significant to retain a clear, user-oriented description of system for use in validation of completed software, and also for reference during maintenance phase of object modeling.