This paper deals with two relevant aspects of the Supervisory Control Problem (SCP) of Discrete Event Systems (DES): the degree of difficulty faced when modeling specifications to be fulfilled by the system under control, and the computational complexity of the synthesis procedure. The presented approach consists in refining the set of events of a DES model into a new set. Each refinement is properly chosen to identify a particular instance of the original event in the system, which may simplify the modeling of specifications. A map named Distinguisher is then proposed to establish the relationship between strings of the original and refined alphabets. It is initially shown that using a refined set of events to solve a SCP directly leads to the optimal control solution, yet without providing computational advantages in synthesis with respect to the nonrefined method. Then, we propose the use of outer-approximations for the refined DES model as a way to reduce the cost of synthesis, while preserving controllability, least restrictiveness and nonblocking of the control solution. Two examples of manufacturing systems illustrate our results. (C) 2015 Elsevier Ltd. All rights reserved.