The Dynamics NAV database
Dynamics NAV 2016 stores its data in a Microsoft SQL database or Azure SQL. NAV 2009 and the earlier versions of Dynamics NAV used either a Microsoft SQL database or a native database for Dynamics NAV. The native database has been discontinued and is no longer available because it's antiquated and has limitations.
The database used by Dynamics NAV is a relational database but it does not fully implement the referential integrity concept that ensures that relationships between tables remain consistent. In Dynamics NAV, data integrity is maintained partially by the database engine itself and mainly by code. Sometimes, it is not even maintained.
Tip
When developing new Dynamics NAV functionalities, consider data integrity inside your analysis and design work.