The interaction of access control and object orientation in extensible systems

The authors describe how object-oriented language design interacts with access control in extensible systems, based on their experience in building the SPIN extensible operating system. Several modern extensible systems, such as Java-enabled Web browsers and SPIN, use object-oriented languages for extensibility. These systems allow extension programs written in their languages (Java and Modula-3, respectively) to be linked in at run-time. The paper presents a case study of the object-oriented language design issues that they encountered in building SPIN. First, they describe how access control in SPIN is affected by the language design choices made in Modula-3, and how they changed Modula-3 to satisfy access control requirements. Second, they compare the access control mechanisms they chose in SPIN, which are mostly link-time, with those in Java, which are mostly compile-time.