Computational and Structural Aspects of Openly Speciied Type Hierarchies
چکیده
One may identify two main approaches to the description of type hierarchies. In total speciication, a unique hierarchy is described. In open speciication, a set of constraints identiies properties of the hierarchy , without providing a complete description. Open speciication provides increased expressive power, but at the expense of considerable computational complexity, with essential tasks being NP-complete or NP-hard. In this work, a formal study of the structural and computational aspects of open speciication is conducted, so that a better understanding of how techniques may be developed to address these complexities. In addition, a technique is presented, based upon Horn clauses, which allows one to obtain answers to certain types of queries on open speciications very eeciently.