In this paper, we discuss an approach to structural objects based on a generalisation of indiscernibility relation used in rough set theory. The existing results in rough set theory are based on the assumption that objects are perceived by attribute value vectors. We propose the new point of view on rough set theory. We replace information systems with the knowledge representation models that incorporate information relative to the structure of objects. We redefine the indiscernibility relation as a relation on objects characterised by some axioms. Such a definition can be naturally applied for information systems with missing values and multivalued attributes. We extend the approach on structural objects. We introduce the meaning representation language for expressing properties of structural objects and we show how to select relevant formulae from this language for sequential data.