Domain Views for Constraint Programming

TL;DR

This paper introduces domain views in constraint programming, simplifying implementation and expanding scope by delegating only domain operations and supporting non-injective views, with demonstrated practical benefits.

Contribution

It proposes domain views as an alternative to variable views, enabling simpler implementation and broader applicability in constraint programming systems.

Findings

Domain views simplify value-based propagation implementation.

They support non-injective views compositionally.

Experimental results show practical performance benefits.

Abstract

Views are a standard abstraction in constraint programming: They make it possible to implement a single version of each constraint, while avoiding to create new variables and constraints that would slow down propagation. Traditional constraint-programming systems provide the concept of {\em variable views} which implement a view of the type $y = f(x)$ by delegating all (domain and constraint) operations on variable $y$ to variable $x$. This paper proposes the alternative concept of {\em domain views} which only delegate domain operations. Domain views preserve the benefits of variable views but simplify the implementation of value-based propagation. Domain views also support non-injective views compositionally, expanding the scope of views significantly. Experimental results demonstrate the practical benefits of domain views.