Before revision:  Unmanned Aircraft Systems (UAS) traffic management system (UTM)is necessary for automated safe and efficient low-altitude airspace operations. FAA has conceptualized the requirements on UTM protocols and components in the FAA's Concept of Operations for UTM report .
After revision:  Unmanned Aircraft Systems (UAS) is the notion of operation volume (OV). An OV is a 4-dimensional block of airspace and time, which can express an aircraft's intent, and can be used for planning, de-confliction, and traffic management. While there are several high-level simulators for UAS Traffic Management (UTM), we are lacking a framework for creating, manipulating, and reasoning about OVs for heterogeneous air vehicles .