On the Expressive Power of String Constraints

We investigate properties of strings which are expressible by canonical types string constraints. Specifically, we consider a landscape 20 logical theories, whose syntax is built around combinations four common elements constraints: language membership (e.g. for regular languages), concatenation, equality between terms, and string-lengths. For variable x formula f from given theory, the set values may be substituted as part satisfying assignment, or in other words, property expresses through x. Since string-based logics, this formal language. firstly relative expressive power different constraints comparing classes languages corresponding able to establish mostly complete picture regard. Secondly, question deciding whether expressed variable/formula one theory can another theory. several negative results relevant preprocessing normalisation practice. Some our have strong connections important open problems regarding word equations solving.