In this paper a formal declarative semantics of the rule-based language mOPS5
is defined. As the name of the language says, it is a simplified version of
OPS5. At first we describe informally this language, the semantics of mOPS5
is then defined in terms of \Datalog-fneg, a logic programming language,
which has a well-defined minimal model semantics and fixpoint semantics. The
availability of a clean semantics has several advantages: it allows program
analysis and optimization as well as judging the correctness of
implementations.