In the recent years, we are witnessing an increasing interest in the Semantic Web and the relevant technologies, which can have a significant impact in the enterprise environment of information and knowledge management. An important observation is that the entity identification problem lies at the core of many semantic web applications. In this paper, we examine the special requirements of storage and management for entities, in the context of an entity management system for the semantic web. We study the requirements with respect to creating and modifying these entities, as well as to managing their evolution over time. Finally, we propose a conceptual model for there presentation of entities, and discuss related research directions.