Database Modeling and Design

76 CHAPTER 4 Requirements Analysis and Conceptual Data Modeling
Department
Contractor
1 1
has
does
R-sec
N
in
1
N
Report
N
1
has
N
R-abbr
1
has
N
Author
N
does
N
Project
(a) ER model before clustering
Department
Contractor
1 1
has
does
Report
N
N Report
Report
(entity cluster)
2.1
Author
N
does
N
Project
(b) ER model after clustering
Figure 4.8
Entity clustering concepts
Report box, but we must retain the name Author, which is not the name
of the entity cluster.
4.5.2 Grouping Operations
Grouping operations are the fundamental components of the entity
clustering technique. They define what collections of entities and relationships
comprise higher-level objects, the entity clusters. The operations
are heuristic in nature and include (see Figure 4.9):