Database Reference
In-Depth Information
WorkerNo
StartDate
DaysWorked
related to
WORKER
WORKSON
related to
WorkerName
BUILDING
BuildingID
Location
BldgType
Figure 7-18
Relationship entity type.
CustNo
CustName
ProdNo
ProdDesc
CUSTOMER
PRODUCT
ShipNumber
NoOfUnits
SHIPMENT
WAREHOUSE
WhseLocation
WhseNo
Figure 7-19
Representing a gerund in E-R model.
Generalization and Specialization
All the points covered in our discussion of generalization and specialization in the
object-based data model apply to the E-R data model. Instead of repeating the dis-
cussion here, it will be worthwhile to refer back to Chapter 6.
We just want to highlight the difference in the notations. Figure 7-20 contains a
partial E-R data model showing an example of generalization and specialization.
Note the notations used according to E-R data model conventions.
Search WWH ::
Custom Search