SEMANTIC DATA MODEL TO RELATIONAL DATA MODEL - Database Design and Development: An Essential Guide for IT Professionals - page 279

ClntNo ContactNo

ContactName

ClntName 1 1

assigns

CONTACT
PERSON

CLIENT

ClntAddr

ContactPhone

Relational Notation

CLIENT ( ClntNo , ClntName, ClntAddr)
CONTACT PERSON ( ContactNo ,ContactName, ContactPhone, ClntNo)
Foreign Key: ClntNo REFERENCES CLIENT

CLIENT relation

ClntNo

ClntName ClntAddr

11111 ABC Industries 6 William Street, Jamesburg, NJ 08810

22222 Progressive Systems 1 Bradford Place, Iselin, NJ 08834

33333 Rapid Development 47 Woods Drive, Edison, NJ 08817

44444 Richard Associates 55 Walker Lane, Metuchen, NJ 08819

Quality Consulting

55555 35 Rues Ave., E. Brunswick, NJ 08821

CONTACT PERSON relation

ContactNo ContactName ClntNo

ContactPhone

123 Mary Williams 732-345-8100 22222

11111
55555

234 Winston Poyser

Lisa Moore

732-555-4000

345 732-767-5300

Figure 9-8 Better transformation of one-to-one relationship.

CustNo OrderNo

OrderDate

CustName 1 *

places

CUSTOMER

ORDER

CustAddr

OrderAmount

1
2
3
4
5
6

1111

1112

1113

Figure 9-9 CUSTOMER and ORDER: one-to-many relationship.

• It does not really matter whether you place the foreign key column in one table
or the other. However, to avoid wasted space, it is better to place the foreign
key column in the table that is likely to have fewer rows.

One-to-Many Relationships

Let us begin our discussion of the one-to-many relationship by reviewing
Figure 9-9. This figure shows the one-to-many relationship between the two objects
CUSTOMER and ORDER.