This part of the book (Chapters 19 through 22) describes the plug-and-play components of PL/Vision. These are pieces of code that can be used as-is in your own applications. Examples include a high-level exception handler mechanism and a generic, reusable logging mechanism.
Chapter 19:
PLVdyn and PLVfk: Dynamic SQL and PL/SQL
Chapter 20:
PLVcmt and PLVrb: Commit and Rollback Processing
Chapter 21:
PLVlog and PLVtrc: Logging and Tracing
Chapter 22:
Exception Handling