RDF (Resource Description Framework) is a World Wide Web Consortium recommendation for specifying meta data models on the web. RDF databases consist of triples in the form of subject-predicate object, which are often conceptualized as defining a directed labeled graph. In this paper, we extend the basic model of RDF by introducing two types of integrity constraints, namely functional and equality generating constraints. Our formal framework is inspired and motivated by the importance of the corresponding constraints in the relational model. In the first part of the paper we present the formal notion of satisfaction for both types of constraints and introduce a mechanism to express functional constraints in terms of equality generating constraints, and we show that the inverse is not possible. In the second part, we define an Armstrong-type scheme of axioms for equality generating constraints and we prove that these axioms form a sound and complete set. In addition, we present chase-like algorithms for both types of constraints that check whether a single constraint follows from a given set of constraints.
Waseem Akhtar, Álvaro Cortés-Calabuig, Jan Paredaens; Constraints in RDF. Proceedings 4th International Workshop on Semantics in Data and Knowledge Bases July 5, 2010, Bordeaux, France. (2010)