Descriptive general frames are duals of modal algebras and, thus, 
provide completeness
for normal modal logics. From the coalgebraic perspective, descriptive 
frames can be represented as coalgebras for the Vietoris functor on the category of 
Stone spaces.
In this talk, I will discuss some model theoretic aspects of descriptive 
frames. In particular,
I will show that many results of classical model theory fail on 
descriptive frames. 
This is joint work with Ian Hodkinson.