Similarity-Based Supervisory Control of Discrete Event Systems
  Due to the appearance of uncontrollable events in discrete event systems, one may wish to replace the behavior leading to the uncontrollability of pre-specified language by some quite similar one. To capture this similarity, we introduce metric to traditional supervisory control theory and generalize the concept of original controllability to $\ld$-controllability, where $\ld$ indicates the similarity degree of two languages. A necessary and sufficient condition for a language to be $\ld$-controllable is provided. We then examine some properties of $\ld$-controllable languages and present an approach to optimizing a realization. 
Yongzhi Cao and Mingsheng Ying