A key challenge of automated planning, including "safe planning," is the requirement of a domain expert to provide the background knowledge, including some set of safety constraints. To alleviate the infeasibility of acquiring complete and correct knowledge from human experts in many complex, real-world domains, this paper investigates a technique for automated extraction of safety constraints by observing a user demonstration trace. In particular, we describe a new framework based on maximum likelihood learning for generating constraints on the concepts and properties in a domain ontology for a planning domain. Then, we describe a generalization of this framework that involves Bayesian learning of such constraints. To illustrate the advantages of our framework, we provide and discuss examples on a real test application for Airspace Control Order (ACO) planning, a benchmark application in the DARPA Integrated Learning Program.