Sequential Relational Decomposition

Authors: Dror Fried, Axel Legay, Joel Ouaknine and Moshe Y Vardi

Paper Information

Title:Sequential Relational Decomposition
Authors:Dror Fried, Axel Legay, Joel Ouaknine and Moshe Y Vardi
Proceedings:LICS PDF files
Editors: Anuj Dawar and Erich Grädel
Keywords:Systems decomposition, Computational thinking, System Composition

ABSTRACT. The concept of decomposition in computer science and engineering is considered a fundamental component of computational thinking and is prevalent in design of algorithms, software construction, hardware design, and more. We propose a simple and natural formalization of sequential decomposition,in which a task is decomposed into two sequential sub-tasks, with the first sub-task to be executed out before the second sub-task is executed. These tasks are specified by means of input/output relations. We define and study decomposition problems,which is to decide whether a given specification can be sequentially decomposed. Our main result is that decomposition itself is a difficult computational problem. More specifically, we study decomposition problems in three settings: where the input task is specified explicitly, by means of Boolean circuits, and by means of automatic relations. We show that in the first setting decomposition is NP-complete, in the second setting it is NEXPTIME-complete, and in the third setting there is evidence to suggest that it is undecidable. Our results indicate that the intuitive idea of decomposition as a system-design approach requires further investigation. In particular, we show that adding human to the loop by asking for a decomposition hint lowers the complexity of decomposition problems considerably.

Talk:Jul 09 11:40 (Session 47D)