With new standards like RDF or OWL paving the way for the much anticipated semantic web, a new breed of large scale semantic systems is about to appear. Even if research on semantic reconciliation methods is abundant, it is not clear how interoperable very large scale semantic systems can be. This paper represents a first effort towards analytically analyzing semantic interoperability in the large: By adapting a recent graph-theoretic framework, we examine the dynamics of large scale semantic systems and derive a necessary condition for fostering global semantic interoperability.