The next ten years will see distributed real-time computersystems replacing many mechanical and hydraulic controlsystems in high-dependability applications. In theseapplications a failure in the temporal domain can be ascritical as a failure in the value domain. This paperdiscusses some of the technology trends that explain whydistributed embedded real-time systems for high-dependability applications will move into the mainstream. Itthen investigates the new requirements that must beaddressed by the software engineering process. Two of themost important requirements are the design forcomposability and the systematic validation of high-dependability distributed real-time systems. In the last twosections, these issues of composability and validation aretreated in some detail.……