XCSP3: An Integrated Format for Benchmarking Combinatorial Constrained Problems
Frederic Boussemart, Christophe Lecoutre, Gilles Audemard, Cédric Piette
TL;DR
XCSP3 presents a comprehensive, integrated intermediate format for benchmarking combinatorial constrained problems, extending XCSP 2.1 with multi-objective optimization, diverse variable domains, and a broad constraint repertoire. It defines a structured, readable representation that preserves model organization through arrays and groups, supports variable views and reification, and offers a dedicated XCSP3-core subset for efficient competition and parsing. The accompanying tool chain links Python/Java modeling libraries to XCSP3 via JSON/XML, enabling reproducible experiments and easy exchange of instances. Together, these features aim to standardize benchmarking across solvers, facilitate cross-tool interoperability, and support advanced reasoning, probabilistic/qualitative frameworks, and soft constraints in a scalable, extensible format.
Abstract
We propose a major revision of the format XCSP 2.1, called XCSP3, to build integrated representations of combinatorial constrained problems. This new format is able to deal with mono/multi optimization, many types of variables, cost functions, reification, views, annotations, variable quantification, distributed, probabilistic and qualitative reasoning. The new format is made compact, highly readable, and rather easy to parse. Interestingly, it captures the structure of the problem models, through the possibilities of declaring arrays of variables, and identifying syntactic and semantic groups of constraints. The number of constraints is kept under control by introducing a limited set of basic constraint forms, and producing almost automatically some of their variations through lifting, restriction, sliding, logical combination and relaxation mechanisms. As a result, XCSP3 encompasses practically all constraints that can be found in major constraint solvers developed by the CP community. A website, which is developed conjointly with the format, contains many models and series of instances. The user can make sophisticated queries for selecting instances from very precise criteria. The objective of XCSP3 is to ease the effort required to test and compare different algorithms by providing a common test-bed of combinatorial constrained instances.