Levelled Entity Relationship Model

Layering ER diagrams has been a key tool to abstract the complexity of large data schemas generated by enterprise modeling. However , the current approaches have a certain impedance between successive steps of reening (or abstracting) ER diagrams. First, most approaches do not have a well-deened correspondence between an entity at a higher level and the entity cluster at a lower level. Second, a relationship to a subentity from an entity in a higher plane is modeled using a relationship which breaks the encapsulation of the entity which contains the subentity. Clearly, it would be nice to have non-encroaching relationships to model such situations. Finally, a reenement (abstraction) step adds (deletes) encroaching relationships and thus cascades changes to the schema beyond the current entity being reened (entity cluster being abstracted). This paper presents the Leveled Entity Relationship Model which demonstrates how one may have an abstraction formalism which does satisfy the above properties.