To date, the Morphware Forum has focused on development of the two-level compile structure and machine model, thus creating a portable development process for compiling basic program units and supporting libraries. However, these elements of the MSI are not sufficient to meet the full set of goals of the PCA program. The Forum is working actively to identify and prioritize the additional services, APIs, and metadata contexts needed for a fully functional PCA system, and to extend the MSI to include them. Extensions that have been discussed include:
· New extensions to program loaders and linkers to support selection and composition of program components from multiple options;
· New operating system (OS) services and calls to support the unique requirements of application morphing at the various levels described in Figure 2;
· A portable resource management system to manage the real-time selection and control of alternative program instantiations;
· A component-based application software architecture; and
· A composable development system that can provide a stable, portable interface to the application programmer while still being customized to the unique lower-level development environment for each PCA architecture.
Once implemented, these MSI services and architectures will support the advanced capabilities made possible by PCA devices. Most fundamental will be the capability to implement morphing across the full spectrum of circumstances detailed in Figure 2 . This in turn is an essential capability to support important end-user system attributes such as validation and verification (V&V) of PCA applications, and real-time fault tolerance in mission-critical applications. For instance, V&V is reported to account for as much as 40 to 70% of system costs [20 ]. The PCA program is seeking to implement a significant portion of the V&V capability in the application build cycle by extending standard techniques with run-time monitoring and checking. Such an approach would likely be significantly integrated with the run-time resource management portion of the MSI. Similarly, the morphing capability of PCA technology offers significant new flexibility in the system response to run-time faults. Utilizing this capability effectively will take advantage of the component-based approach to PCA software and will again require tight integration with the resource management functions.