This paper presents a method for decomposing process-control systems. This decomposition method is automated, meaning that a series of principles that can be evolved to support automated tools are given to help a designer decompose complex systems into a collection of simpler components. Each component resulting from the decomposition process can be designed and implemented independently of the other components. Also, these components can be tested or verified by the end-user independently of each other. Moreover, the system properties, such as safety, stability, and reliability, can be mathematically inferred from the properties of the individual components. These components are referred to as IDEAL (independently developable end-user assessable logical) components. This decomposition method is applied to a case study specified by the High-Integrity Systems group at Sandia National Labs, which involves the control of a future version of the Bay Area Rapid Transit (BART) system.