Input-Output Disjointness for Forward Expressions in the Logic of Information Flows

Last year we introduced the logic FLIF (forward logic of information flows) as a declarative language for specifying complex compositions of information sources with limited access patterns. The key insight of this approach is to view a system of information sources as a graph, where the nodes are valuations of variables, so that accesses to information sources can be modeled as edges in the graph. This allows the use of XPath-like navigational graph query languages. Indeed, a well-behaved fragment of FLIF, called io-disjoint FLIF, was shown to be equivalent to the executable fragment of first-order logic. It remained open, however, how io-disjoint FLIF compares to general FLIF. In this paper we close this gap by showing that general FLIF expressions can always be put into io-disjoint form. 2012 ACM Subject Classification Software and its engineering → Semantics; Software and its engineering → Data flow languages; Theory of computation → Database query languages (principles)