$\aleph_0$-categorical structures with a predimension

We give an axiomatic framework for the non-modular simple $\aleph_0$-categorical structures constructed by Hrushovski. This allows us to verify some of their properties (weak elimination of imaginaries, simplicity, the nature of forking, CM-triviality and stable forking) in a uniform way, and to show that these properties are preserved by iterations of the construction.