This is a nice historical summary of the origin and evolution of MUMPS. The author briefly mentions the involvement of BBN and the JOSS language, but there was actually more. Jordan Baruch, who was a doctoral student of Prof. Leo Beranek, one of the founders of BBN, was involved in the development of what we call a medical information system today, as an employee of BBN and in cooperation with the Massachusetts General Hospital (see https://www.nae.edu/29722/Dr-Jordan-J-Baruch and https://dl.acm.org/doi/10.1145/41526.41531). He switched to the new MEDINET department of General Electric in 1966, where he developed the FILECOMP language, which actually pioneered the tree-based data model where files could be accessed via nested subscripts. This was an important influence on MUMPS.