postgresql – The design of the database implementing the notifications using multiple foreign keys, accepting the Null / None values

I have the following entities:

Account, Owner_TA, Owner_TB, Pub, Item, Event, RTX

Owner_TA and OWNER_TB have a foreign key to the account
Pub and Event have a foreign key to Owner_TB
The element has a foreign key to the owner_TA
RTX has a foreign key to Owner_TA and a proprietary TB

I need help for database design (Postgress 10)

When something happens I have to write a notification

For example,

1. An event is created. In a notification table, I have:


Account | Owner_TA | Owner_TB | Pub | Article | Event | RTX | verb
1 None 2 None None 3 No c


2. An item is updated

Account | Owner_TA | Owner_TB | Pub | Article | Event | RTX | verb
1 3 None None 5 None None U

3. an Owner_TA is updated

Account | Owner_TA | Owner_TB | Pub | Article | Event | RTX | verb
1 3 None None None None None U


4. an account is created

Account | Owner_TA | Owner_TB | Pub | Article | Event | RTX | verb
5 None None None None None None

I want the notification to be something like:

Delta_Name account, for Owner_TA Paul_name, has updated an ITEM,
name of the article;

This is the best approach? And if an object is deleted?