Meaningful modeling: What's the semantics of "semantics"?

Researchers differ on what constitutes semantics for UML subsets and adaptations. Worse, implicit assumptions often influence these definitions and results, which makes comparing published research on UML semantics difficult. The authors have thus set out to clarify some of the notions involved in defining modeling languages, with an eye toward the particular difficulties arising in defining UML. They are primarily interested in distinguishing a language's notation, or syntax, from its meaning, or semantics, as well as recognizing the differences between variants of syntax and semantics in their nature, purpose, style, and use.