feat: Extend table inheritance article

The feedback from Hamburg was, that the single inheritance article
should be more focused on the options, pros and cons of single table
inheritance and define the single_table_inheritance as default and not
as absolute and only correct option.

Author: Fabian Baumeister

modules/ROOT/pages/persistence/jpa.adoc

@@ -63,9 +63,13 @@ Always override the default of the relationship annotation by providing the sele
 
 Mapping enums to their ordinal or name is fragile when it comes to code changes and refactoring. Define a dedicated link:https://www.baeldung.com/java-enum-values#adding-constructor[string in each enum value] for database representation. Enums then have to be treated as a custom datatype with a converter.
 
-=== Use single table inheritance
+=== Entity inheritance
 
-There are several ways to handle link:http://openjpa.apache.org/builds/1.0.4/apache-openjpa-1.0.4/docs/manual/jpa_overview_mapping_inher.html#jpa_overview_mapping_inher_tpc[inheritance in databases]. In most cases, 'single table' should be used, because it is usually the fastest way to do the mapping, as no joins are needed when retrieving, searching or persisting entities. 
+As a good practice it is recommended to avoid entity hierarchies at all where possible and otherwise to keep the hierarchy as small as possible.
+If an hierarchy in the entities is needed, JPA defines several inheritance mechanisms, that are described link:https://en.wikibooks.org/wiki/Java_Persistence/Inheritance[here]. 
+In most cases, `single table` is a good choice, because it is usually the fastest way to do the mapping, as no joins are needed when retrieving, searching or persisting entities. 
+Moreover it is rather simple and easy to understand. 
+One major disadvantage is that the this approach can lead to huge tables with a lot of null values.
 
 == Accessing the data