What are main differences between URM and CoM?
• COM and URM are similar in their common goal to provide a mechanism for logical navigation where we specify only criteria of the query and the target while the system itself finds an appropriate intermediate steps and builds the final access path (in the case of altermative access paths we need to provide more information to avoid ambiguity). • In order to solve the problem of logical navigation and access path independence both approaches assume that the model is characterized by some final semantics. In URM it is called the universal relation while in COM it is called the primitive semantics. This assumption distinguishes these two approaches from other models including the relational model where the final semantics is not defined. • Instead of unique attributes names in URM we use dimensions of arbitrary rank as sequences of dimensions of rank 1. For example, an attribute EmployeesName is written in COM as Employees.Name. • COM relies on the mechanism of inverse dimensions which a
