An original approach to integrate information is considered. In the frame of this approach an extensible canonical model is created which is based on the algebraic model of an advanced XML data model. We consider the canonical model as an intermediate model for creating our mediator and this model has been formalized by means of the Abstract Machine Notation (AMN). For each source model we formalize it by means of the AMN and create a reversible mapping into an extension of the canonical model. After this B-technology is used to prove that the AMN semantics of the source model represents a refinement of the AMN semantics of the extended canonical model. Hereby the correctness of mapping and the ability to use extended canonical model for representation of schemas of the source model are proved. Finally, in order to illustrate our approach a mapping from relational data model to canonical model has been created.