Sort-Stratified Semantics for Temporal Conflict Detection in ODRL Policies
For policy engineers and ODRL users, this provides a sound method to detect temporal conflicts in rights expressions, addressing a fundamental ambiguity in the standard.
The paper addresses unsound conflict detection in ODRL policies due to ambiguous temporal operators, and resolves it via sort stratification that types temporal operands as instants or durations, reducing conflict to interval comparison with a three-valued verdict. The approach is proven sound and evaluated on a benchmark of policy problems.
In the Open Digital Rights Language (ODRL), temporal constraints range over two sorts, instants and durations, but the comparison operators do not distinguish them. The same operator thus means "earlier instant" or "shorter duration," leaving conflict detection between two policies unsound. We resolve this by sort stratification: each temporal operand is typed to one of two ordered domains, points in time or amounts of time. Each constraint then denotes an interval, and conflict reduces to interval comparison under a three-valued verdict (Conflict, Compatible, Unknown). We characterise the check's decidability across a static and a runtime fragment, prove it sound, and evaluate it on a benchmark of policy problems compiled to TPTP and SMT-LIB, available as an artefact.