In recent years, workflows have been increasingly used in scientific applications. This paper presents novel metadata reasoning capabilities that we have developed to support the creation of large workflows. They include 1) use of semantic web technologies in handling metadata constraints on file collections and nested file collections, 2) propagation and validation of metadata constraints from inputs to outputs in a workflow component, and through the links among components in a workflow, and 3) sub-workflows that generate metadata needed for workflow creation. We show how we used these capabilities to support the creation of large workflows in an earthquake science application.