docs: single table inheritance and singleton diagrams

Author: iluwatar

Diff for: single-table-inheritance/README.md

@@ -36,6 +36,10 @@ Wikipedia says
 
 > Single table inheritance is a way to emulate object-oriented inheritance in a relational database. When mapping from a database table to an object in an object-oriented language, a field in the database identifies what class in the hierarchy the object belongs to. All fields of all the classes are stored in the same table, hence the name "Single Table Inheritance".
 
+Flowchart
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+![Single Table Inheritance flowchart](./etc/single-table-inheritance-flowchart.png)
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 ## Programmatic Example of Single Table Inheritance Pattern in Java
 
 Single Table Inheritance is a design pattern that maps an inheritance hierarchy of classes to a single database table. Each row in the table represents an instance of a class in the hierarchy. A special discriminator column is used to identify the class to which each row belongs.

Diff for: single-table-inheritance/etc/single-table-inheritance-flowchart.png

@@ -33,6 +33,10 @@ Wikipedia says
 
 > In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system.
 
+Sequence diagram
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+![Singleton Pattern sequence diagram](./etc/singleton-sequence-diagram.png)
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 ## Programmatic Example of Singleton Pattern in Java
 
 Joshua Bloch, Effective Java 2nd Edition p.18