Code clones are recurring similar program structures. Several techniques exist to detect similar code fragments (simple clones) for better software maintenance, but further gains can be obtained by by detecting similar classes, source files or directories. Structural clones embody such large-granularity, design-level similar program structures that often map to design or application domain concepts. Detection of structural clones leads to a better understanding of the design of the system, easing software maintenance, evolution, and re-engineering. Unification of structural clones ...