We know that DCFL is not closed under the union operation and CFL is closed under union and contains the union of DCFLs.
Is there a characterization of finite unions of DCFLs?
One direction is clear: the union of any finite number of DCFL's is a CFL.
However, a precise characterization of the union-closure of DCFL's was not obvious to me at all (and I teach this stuff and wrote a book on it), so I went searching with a google search. I found this paper by my colleagues Martin Kutrib and Andreas Malcher: Context-Dependent Nondeterminism for Pushdown Automata, O.H. Ibarra and Z. Dang (Eds.): DLT 2006, LNCS 4036, pp. 133–144, 2006. Theorem 1 gives a characterization of this class.
DCFLs not closed under union hence we will see language higher than DCFLs in Chomsky's classification hierarchy CFLs are closed under union hence union of two DCFL if not DCFL then CFL you can take the example of a^nb^n and a^2n b^n.