Structure-Aware Encodings of Argumentation Properties for Clique-width
This work addresses the challenge of understanding encoding capabilities for clique-width in computational complexity, specifically for abstract argumentation, which is incremental as it extends known methods to a more general parameter.
The paper tackles the problem of encoding abstract argumentation problems into (Q)SAT while preserving clique-width, a graph parameter, and designs novel reductions that linearly maintain clique-width, establishing results for all argumentation semantics including counting, with overhead that cannot be significantly improved under reasonable assumptions.
Structural measures of graphs, such as treewidth, are central tools in computational complexity resulting in efficient algorithms when exploiting the parameter. It is even known that modern SAT solvers work efficiently on instances of small treewidth. Since these solvers are widely applied, research interests in compact encodings into (Q)SAT for solving and to understand encoding limitations. Even more general is the graph parameter clique-width, which unlike treewidth can be small for dense graphs. Although algorithms are available for clique-width, little is known about encodings. We initiate the quest to understand encoding capabilities with clique-width by considering abstract argumentation, which is a robust framework for reasoning with conflicting arguments. It is based on directed graphs and asks for computationally challenging properties, making it a natural candidate to study computational properties. We design novel reductions from argumentation problems to (Q)SAT. Our reductions linearly preserve the clique-width, resulting in directed decomposition-guided (DDG) reductions. We establish novel results for all argumentation semantics, including counting. Notably, the overhead caused by our DDG reductions cannot be significantly improved under reasonable assumptions.