The EPOS Database [Mun93] is a general-purpose DBMS with
features geared for SCM. All objects are versioned
according to our COV versioning model [MLG+93], which we will not
discuss in this paper.
The EPOSDB uses an extended ER data model with subtyping. There is a predefined type longfield; instances of this type have additional operations for checkin/ checkout of the file contents to/ from normal UNIX files. In addition to ``normal'' objects, the EPOSDB also maintains user-queriable objects representing all types, active transactions, future transactions as defined in TiDL (see below), etc.