  One of the most utilized data mining tasks is the search for association
rules. Association rules represent significant relationships between items in
transactions. We extend the concept of association rule to represent a much
broader class of associations, which we refer to as \emph{entity-relationship
rules.} Semantically, entity-relationship rules express associations between
properties of related objects. Syntactically, these rules are based on a broad
subclass of safe domain relational calculus queries. We propose a new
definition of support and confidence for entity-relationship rules and for the
frequency of entity-relationship queries. We prove that the definition of
frequency satisfies standard probability axioms and the Apriori property.
