We formalize a string analysis within abstract interpretation framework. The abstraction of strings is given as a conjunction of predicates that describes the common configuration changes on the reference pushdown automaton while processing the strings. We also present a family of pushdown automata called E bounded pushdown automata. This family covers all context-free languages, and by using this family of pushdown automata, we can prevent abstract values from becoming infinite conjunctions and guarantee that the operations required in the analyzer are computable.