The words, Database and Relational are often considered as synonyms. Not only is that not true, database preceded “Relational” by about 25 years. Additionally, the Database Management Systems (DBMSs) that conformed to the precepts of the relational model passed from existence in about the year 2000. That’s because the SQL-1999 standard contained features that are clearly not relational. Thus, SQL-based DBMSs that claim conformance to this standard are too no longer “Relational.”
The biggest addition to the SQL Standard was database object classes. These enable the definition of complex data structures and supporting methods, triggers and stored procedures to process these complex structures.
SQL:1999 thus incorporated many of the features of the 1960s and 1970s DBMSs. That is, hierarchies, networks, complex relationships, and embedded pointers between data records (rows) within and across database tables.
Because of these additions, ISO/ANSI Standard SQL, starting in 1999, became its own data model with a unique set of record structures, relationships and operations. It is these additions that enable database object classes, which, in turn enable the return of the very sophisticated database structures, processes and processing that were so common in the 1960s through the 1980s that disappeared with the advent of “Relational.”