From failure to success : comparing a denotational and a declarative semantics for Horn clause logic

The main purpose of the paper is to relate different models for Horn clause logic: operational, denotational, declarative. We study their relationship by contrasting models based on interleaving, on the one hand, to models based on maximal parallelism, on the other. We make use of complete metric spaces as an important mathematical tool, both in defining and in comparing the various models.