Workflow technology has emerged as one of those technologies designed to support modeling, designing and executing business processes. One of the major limitations of current workflow management systems is the lack of flexibility to support dynamic management of workflows. In this paper, we propose a dynamic workflow management model based on web services. We integrate web services and ontology technologies to support dynamic specifying, monitoring, analyzing, designing, configuring and executing workflows. We explain the need and functionality of the main modules and interfaces of the model, and introduce its application in a case study. An important feature of this model is to support for planning and adaptive workflow management.