Interactive Distributed Configuration

Interactive conflguration is the concept of assisting a user in selecting values for parameters that respect given constraints. It was originally inspired by the product conflguration problem with the emer- gence of the mass-customisation paradigm in product manufacturing, but has also been applied to other tasks requiring user interaction, such as specifying services or setting up complex equipment. The user-friendly requirements for complete, backtrack-free and real-time interaction makes the problem computationally challenging. In this paper we look at the concept of distributed conflguration, where similar user functionality should be provided in a distributed environ- ment, where knowledge about constraints and variables is fragmented over several nodes, each node exchanging information through message passing. We develop a theoretical model, formalise the problem, and sug- gest a solution approach that uses techniques from the area of Constraint Satisfaction and utilises a compilation scheme based on Binary Decision Diagrams (BDD) (1). Interactive conflguration problems are special applications of Constraint Satis- faction Problems (CSP) where a user is assisted in interactively assigning values to variables by a software tool. This software, called a conflgurator, assists the user by calculating and displaying the available, valid choices for each unassigned variable in what are called valid domains computations. Application areas in- clude customising physical products (such as PC's and cars) and services (such as airplane tickets and insurances). Three important features are required of a tool that implements interactive conflguration: it should be complete (all valid conflgurations should be reachable through user interaction), backtrack-free (a user is never forced to change an earlier choice due to incompleteness in the logical deductions), and it should provide real-time performance (feedback should be fast enough to allow real-time interactions). The requirement of obtaining backtrack-freeness while maintaining completeness makes the problem of calculating valid domains NP-hard. The real-time performance requirement enforces further that runtime calculations are bounded in polynomial time. According to user-interface design criteria, for a user to perceive interaction as being real-time, system response needs to be