OBJECT-BASED DATA MODEL: PRINCIPLES AND COMPONENTS - Database Design and Development: An Essential Guide for IT Professionals - page 181

CustName

OrdDate

CustAddr OrdNo

CustNo

CUSTOMER places ORDER

*

1

1

OrdAmt

contains

*

PRODUCT

ProdID

UnitPrice

ProdDesc

Figure 6-6 Relationships: CUSTOMER, ORDER, PRODUCT.

CUSTOMER ORDER

PRODUCT

Figure 6-7 Relationships: links between instances.

object boxes simply indicates that the instances are related with one another. The
name of the relationship as written within the diamond applies to each link between
instances.

Cardinality in Relationships

You now clearly understand that relationships between two objects indicate the
associations of instances of one object with instances of a second object. Let us take
the example of the relationship between the objects CUSTOMER and ORDER.
The relationship exists because a customer places one or more orders. Examine this
relationship. Let us say that customer Techchoice, Inc. has placed four orders and