Fault tolerance (FT) is a topic of major concern in achieving dependable systems, for both real-time as well as non-real-time systems. This paper provides a model of achieving fault tolerance, based on the ISO/ITU Reference Model for Open Distributed Processing (RM-ODP). This reference model provides a system software engineering methodology for fault tolerance, an object based model of fault tolerance, system requirements for achieving fault tolerance in an open manner 1, modeling constructs and rules to enable a proper system specification of fault tolerance, and business rules in terms of policies to achieve a well-formed system specification. All these aspects are discussed at some depth in this paper, but primarily focused on how certain behavior can be specified and achieved in an object-based system, using the constructs of the Unified Modeling Language (UML) and Object Constraint Language (OCL).