Sesqui-pushout (
Sq
PO)
rewriting—“sesqui” means “one and a half” in Latin—is a new algebraic approach to abstract rewriting in any category.
Sq
PO rewriting is a deterministic and conservative extension of double-pushout (
dpo) rewriting, which allows to model “deletion in unknown context”, a typical feature of single-pushout (
spo) rewriting, as well as cloning.
After illustrating the expressiveness of the proposed approach through a case study modelling an access control system, we
discuss sufficient conditions for the existence of final pullback complements and we analyze the relationship between SqPO and the classical dpo and spo approaches.
Research partially supported by EPSRC grant GR/T22049/01, DFG project sands, EC RTN 2-2001-00346 SegraVis, EU IST-2004-16004 SEnSOria, and MIUR PRIN 2005015824 ART.