A Programmable Client-Server Model: Robust Extensibility via DSLs

The client-server model has been successfully used to support a wide variety of families of services in the con-text of distributed systems. However, its server-centric na-ture makes it insensitive to fast changing client character-istics like terminal capabilities, network features, user pref-erences and evolving needs. To overcome this key limitation, we present an approach to enabling a server to adapt to different clients by making it programmable. A service-description language is used to program server adaptations. This language is designed as a domain-specific language to offer expressiveness and conciseness without compromising safety and security. We show that our approach makes servers adaptable without requiring the deployment of new protocols or server imple-mentations. We illustrate our approach with the Internet Message Access Protocol (IMAP). An IMAP server is made pro-grammable and a language, named Pems, is introduced to program robust variations of e-mail services. Our approach is uniformly used to develop a platform for multimedia communication services. This platform is composed of programmable servers for telephony services, e-mail processing, remote-document processing and stream adapters. 1