We present a generic aproach to the static analysis of concurrent programs
with procedures. We model programs as communicating  pushdown systems. It 
is known  that typical dataflow problems for this model are undecidable, 
because the emptyness problem for the intersection of context-free  languages, 
which is undecidable, can be reduced to them. In this paper we propose  an 
algebraic framework for defining upper approximations of context-free languages. 
The approximations belong to different classes of commutative languages, i.e. 
languages that contain a word if and only if they contain all its permutations.  
We show how to compute such approximations by combining automata theoretic 
techniques with algorithms for solving systems of polynomial inequations in 
commutative Kleene algebras.