  In this paper we present a new approach to data modelling, called the
concept-oriented model (CoM), and describe its main features and
characteristics including data semantics and operations. The distinguishing
feature of this model is that it is based on the formalism of nested ordered
sets where any element participates in two structures simultaneously:
hierarchical (nested) and multi-dimensional (ordered). An element of the model
is postulated to consist of two parts, called identity and entity, and the
whole approach can be naturally broken into two branches: identity modelling
and entity modelling. We also propose a new query language with the main
construct, called concept, defined as a pair of two classes: identity class and
entity class. We describe how its operations of projection, de-projection and
product can be used to solve typical data modelling tasks.
