Like any other software artifact, models evolve and need to be versioned. In the last few years, dedicated support for model versioning has been proposed to improve the default text-based versioning that version control systems offer. However, there is still the need to comprehend model differences in terms of the semantics of the modeling language. For this purpose, we propose a comprehensive approach that considers both abstract and concrete syntax, to express model differences in terms of the domain-specific language (DSL) used and define domain-specific semantics for specific difference patterns. The approach is based on the automatic extension of the DSL to enable the representation of changes, on the definition of rules to capture recurrent domain-specific difference patterns, and on the automatic adaptation of the graphical concrete syntax to visualize the differences. We present a prototype tool support and discuss its application on versioned models created by third parties.