Section: New Results

Specific studies: active documents and web services

Participants : Albert Benveniste, Loïc Hélouët, Sundararaman Akshay.

Active Documents have been introduced by the GEMO team at Inria Futurs, headed by Serge Abiteboul, mainly through the language Active XML (or AXML for short). AXML is an extension of XML which allows to enrich documents with service calls or sc's for short. These sc's point to web services that, when triggered, access other documents; this materialization of sc's produces in turn AXML code that is included in the calling document. One therefore speaks of dynamic or intentional documents. In the past years, we have collaborated with the GEMO team to study a distributed version of their language.

Last year, we have developed a distributed Active XML engine, which can be distributed over a network. We have built a lightweight experimentation platform, made of four Linux machines, that run DAXML services and communicate with one another. This year, we have started an experiment with a case study. We have proposed a distributed chess service palteform; the main idea is to use choreographies to provide solutions for chess problems, relying on an orchestration of specialized services for different phases of a game (opening, end of game, or collecting positions databases. We expect preliminary results in 2013.

Last year, we have proposed a new model, that combines arbitrary numbers of finite workflows, hence allowing for the definition of sessions. Sessions is a central paradigm in web-based systems. As messages exchange between two sites need not follow the same route over the net, a site can not rely on the identity of machines to uniquely define a transaction. This unique identification is essential: a commercial site, for instance, needs to manage several interactions at a given time. The current trend, as in BPEL, is to associate a unique identifier with each session. Modeling realistic sessions hence often forces to include session counters, and hence render most of properties undecidable. The session formalism studied in 2011 can be seen as a mix of BPEL and Orc elements, but was designed to keep several properties decidable (the formalism has the expressive power of reset Petri nets). The strength of this formalism is to allow designing systems that use sessions without the obligation to provide identifiers. Its drawback is that it only allows for the design of systems with a fixed number of agents. This year, we have continued extending last year's work with Ph. Darondeau from the S4 Team, and with M. Mukund from the Chennai Mathematical Institute to allow design of systems with sessions and allowing for an arbitrary number of agents.