Extending ER Model Clustering by Relationship Clustering

The entity relationship approach is a widely accepted method for conceptual database design. However, some problems arise if ER modelling is applied to the design of really large databases concerning whole enterprises. There is, e.g., no way to obtain a general view nor to perceive the global context of a detailed enterprise scheme with hundreds of entity and relationship types. Different approaches use the method of ER model clustering to overcome these problems. Whole sections of the detailed diagram are mapped into so-called entity-clusters, which are presented as (complex) entity types in a higher level ER diagram. All approaches are based on an already existing detailed ER diagram. Based on this, the abstraction layers are built bottom-up. The approach proposed in this paper refines and extends the approaches mentioned above. It also takes into account the Nested Entity Relationship Model in order to refine relationship types. It can be used in a top-down database design process as well as in a bottom-up approach. Furthermore standard diagrams for industry branches can be designed and individually refined for a specific enterprise.