Comment by odyssey7

MUMPS appeared in 1966, predating Edgar Codd's 1970 paper that would later give rise to relational databases. Additions to SQL introduced by the 1992 ANSI standard have become essential to its modern form.

So, although NoSQL is a familiar framing, pre-SQL is a more appropriate designation for MUMPS, since NoSQL was a response to SQL.

The tree data structure used by MUMPS is specifically a B-tree. This is a standard data structure and doesn't on its own give MUMPS much to brag about over other DBMSs which offer B-trees. MySQL offers B-trees as an indexing option, for instance.