We propose a programming language, Flage, for building software systems which dynamically adapt to changing local situations. In our language, we construct applications by agents; concurrent mobile objects with the metalevel architecture. Metalevel programming facilities realize a self-control of an agent's actions and an autonomous adaptation to changes. We also introduce another kind of program element called field. A field represents a local situation around agents. For example, one field represents a virtual place to get local information in a network environment and another represents a virtual place where agents do cooperative works. If an agent enters a field, it gets programs and shared information in the field. By moving field to field, an agent can change its program composition by itself and it adapts to changing local situations. In this paper, we describe the language specification of Flage, the implementation of the platform for Flage programming and show some program examples.

This paper describes the architecture to implement an application in network environments, which adapts to unexpected change in the development phase. In this architecture, an application is expressed as an agent which consists of two layers: base level and meta level. The base level program is an application program and the meta level program is the program that controls the execution of the base level and changes the base level program. Virtual places are also provided in the network. They are used for the release of programs and information which agents retrieve to change their own base level program. An application (or an agent), when a change is required, moves from places to places for the retrieval of programs to adapt to the change. A program search strategy is introduced to adapt to changes by using distributed thesauri of released programs, which realizes an agent's program retrieval method in network environments.