How does Alloy differ from other languages?

Unlike a programming language, an Alloy model is declarative: it can describe the effect of a behaviour without giving its mechanism. This allows very succinct and partial models to be constructed and analyzed. It is similar in spirit to the formal specification languages Z, VDM, Larch, B, OBJ, etc, but, unlike all of these, is amenable to fully automatic analysis in the style of a model checker.