完整word版数据库系统基础教程第四章答案

Solutions

Chapter 4

4.1.

1

4.1.2

b)

c)

In c we assume that a phone and address can only bel ong to a sin gle customer (1-

d)

In d we assume that an address can only bel ong to one customer and a phone can exist at only one address.

If the multiplicity of above relati on ships were m-to-n, the en tity set becomes weak and the key ssNo of customers will be needed as part of the composite key of the en tity set.

In c&d, we convert attributes phones and addresses to entity sets. Since entity sets often become relations in relational design, we must con sider more efficie nt alter natives.

In stead of query ing multiple tables where key values are duplicated, we can also modify attributes:

(i)P hones attribute can be con verted into HomePho ne, OfficePh one and CellPh one.

(ii) A multivalued attribute such as alias can be kept as an attribute where a sin gle colu mn can be used in relati onal desig n i.e. con cate nate all values. SQL

4.1.3

4.1.4

a)

c)

The relati on ship "played" betwee n Teams and Players is similar to relati on ship "plays" betwee n Teams and Players.

b) 1 >: i .-I T mains Oo L UJT 曰 Pla.yor3

uid^r 4.1.5 I ■

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4.1.6 The in formatio n about childre n can be ascerta ined from motherOf and fatherOf relati on ships. Attribute ssNo is required since n ames are not uni que.

People

4.1.7