Production of reliable and flexible distributed applications is a growing area of interest and research. Various middleware technologies are often used as the communication infrastructure and as a practical ease to the network programming problem. Among them, message-oriented middleware (MOM) are known to provide reliable and flexible communication through asynchronous message passing. This kind of middleware is of particular interest when coordinating components that are not designed for simultaneous execution. Usually MOM focus on the communication layer with a programming interface, charge to the external components to adapt to the MOM communication model. We introduce a distributed programming model based on autonomous software entities called agents. Agents act as the glue software components and they offer reliable and flexible properties like atomic execution or migration from node to node. The combination of both a MOM and agents has been implemented in the AAA platform presented in the second part of the paper.

The purpose of the Guide project is to explore the use of shared objects for communication in a distributed system, especially for applications that require cooperative work. Since 1986, two prototypes have been implemented respectively on top of Unix (Guide-1) and Mach 3.0 (Guide-2). They have been used for the development of distributed cooperative applications, allowing us to validate or reject many design choices in the system.

The Guide language is an object-oriented language dedicated for programming distributed applications on top of the Comandos platform. This language faithfully reflects all the capabilities of the Comandos model. It combines the facilities of a strongly typed object model with a powerful computational model. Key features of the language are: separation between types and classes, conformant subtyping, distribution transparency, concurrent activities, synchronization mechanism for shared objects, and exception handling. This paper presents the design choices for the Guide language and discusses programming experience gained from the use of the language for the construction of distributed applications.