Caché ObjectScript (COS) is a part of the Caché database system sold by InterSystems. The language is a functional superset of the ANSI-standard MUMPS programming language. Since Caché is at its core a MUMPS implementation, it can run ANSI MUMPS routines with no change. To appeal as a commercial produce, Caché implements support for object-oriented programming, a macro preprocessing language, embedded SQL for ANSI-standard SQL access to M's built-in database, procedure and control blocks using C-like brace syntax, procedure-scoped variables, and relaxed whitespace syntax limitations.
The language has private and public variables and globals. Global has a different meaning in this language than in most; such variables are global across routines, processes, and sessions. Thus, editing a global variable is making permanent and immediate changes to a system-universal database (which survives reboots, etc.). The scope of a private variable is the local function, the scope of a public variable is the entire process. Variables, private and public, may be single elements or complete multi-dimensional arrays.
The great majority of Caché's feature-set is inherited from the ANSI MUMPS standard. See that article for details on how data is represented and the different ways a programmer can think about the data during development.