On the second chart, a more prudent developer might consider the System Design as also Critical and Implementation as requiring a Caution. There is no fixed definition but experience has shown that software developers usually overestimate the amount accomplished and underestimate the amount of time needed to finish. Object models, data flow diagram, semantic data models as needed. Describe the design method. This provides an Architectural Design of the subpart and is a new section of the document.
Object diagrams describing scenarios are appropriate.
The bottom level of the design provides the specifications for the top-level of the implementation. Examples may be given. Overview major phases of the testing process from unit testing to system testing. Include validating requirements and acceptance testing. List tested items organized by phases.