  Assurance cases are used to demonstrate confidence in system properties of
interest (e.g. safety and/or security). A number of system assurance approaches
are adopted by industries in the safety-critical domain. However, the task of
constructing assurance cases remains a manual, trivial and informal process.
The Structured Assurance Case Metamodel (SACM) is a standard specified by the
Object Management Group (OMG). SACM provides a richer set of features than
existing system assurance languages/approaches. SACM provides a foundation for
model-based system assurance, which has great potentials in growing technology
domains such as Open Adaptive Systems. However, the intended usage of SACM has
not been sufficiently explained. In addition, there has been no support to
interoperate between existing assurance case (models) and SACM models. In this
article, we explain the intended usage of SACM based on our involvement in the
OMG specification process of SACM. In addition, to promote a model-based
approach, we provide SACM compliant metamodels for existing system assurance
approaches (the Goal Structuring Notation and Claims-Arguments-Evidence), and
the transformations from these models to SACM. We also briefly discuss the tool
support for model-based system assurance which helps practitioners to make the
transition from existing system assurance approaches to model-based system
assurance using SACM.
