PLANET: an open mobile object system for open network

Mobile objects (or mobile agents) attract the attention of many researchers in many network-related research areas. Despite the broad attraction, the implementation schemes of mobile object systems are inclined to adopt a programming language-centric approach; that is, the functionality of mobile object computing is so tightly incorporated into the design of a brand new programming language that users are obliged to use the single programming language. Besides the programming-language-centricity, there is another trend in most current mobile object systems: bytecode-interpretation-basis, whereby the state of objects and/or computation activity can be handled in a straightforward and neat way, the platform-heterogeneity can be easily dealt with, and security handling is not difficult in principle. However, there are several reasons why the above-mentioned currently dominant approach is not sufficient. We are designing and implementing the PLANET mobile object system that has quite a different approach (K. Kato et al., 1997). PLANET is designed to be open, which means that the system is designed as a middleware between the operating system layer and the programming language system layer and is designed to be neutral to the designs of programming languages and bytecodes. It is also designed to be used in an open network environment such as the Internet. PLANET provides the following functions: unloading memory segments which contain a mobile object from a virtual address space, transferring those memory segments to another computer site efficiently, loading it into a virtual address space there, and continuing its execution under rigorous but flexible protection control