Better approximation guarantees for job-shop scheduling

Job-shop scheduling is a classical NP-hard problem. Shmoys, Stein, and Wein presented the rst polynomial-time approximation algorithm for this problem that has a good (polylogarithmic) approximation guarantee. We improve the approximation guarantee of their work and present further improvements for some important NP-hard special cases of this problem (e.g., in the preempti ve case where machines can suspend work on operations and later resume). We also present NC algorithms with improved approximation guarantees for some NP-hard special cases.