Derive concrete classes from the preceding abstract domain definition.

Validate: Add a validation function, including security enforcement.  Use JSON schemas to enforce a language-agnostic message definition which should cover 90 to 95% of validation rules. Add functions to validate class for the remaining 5 to 10%.

QueueController:  Accepts a Msg_ID, creates a queue if necessary.  Has two methods, get and put.  Maybe a remove.

AbstractAction: Base class for all actions.  Needs to reference JSON Schemas, too, particularly for Msg_EXT info.

DAO: Standard data access object with CRUD functions for various tables - user, account, history, etc.