The org.apache.sis.metadata.sql package takes advantage of table inheritance as documented there:
However as of version 9.6, PostgreSQL does not support index inheritance. This limitation is documented in the "Caveats" section at the bottom of the above-cited page. The consequence is that org.apache.sis.metadata.sql can not enforce foreigner key constraints on columns that reference a parent table.
If PostgreSQL supports index inheritance in a future version, then the Dialect.isIndexInheritanceSupported constant should be set to true.