文档介绍：.
精选文档.
Solutions
Chapter 4

a)
b)
.
精选文档.
c)
In c we assume that a phone and address can only belong to a single customer (1-m relationship represented by arrow into customer).
.
精选文档.
d)
In d we assume that an address can only belong to one customer and a phone can exist at only one address.
If the multiplicity of above relationships were m-to-n, the entity set becomes weak and the key ssNo of customers will be needed as part of the composite key of the entity set.
In c&d, we convert attributes phones and addresses to entity sets. Since entity sets often become relations in relational design,
we must consider more efficient alternatives.
Instead of querying multiple tables where key values are duplicated, we can also modify attributes:
(i) Phones attribute can be converted into HomePhone, OfficePhone and CellPhone.
(ii) A multivalued attribute such as alias can be kept as an attribute where a single column can be used in relational design . concatenate all values. SQL allows a query "like '%Junius%'" to search the multiple values in a column alias.

.
精选文档.

a)
.
精选文档.
b)
c)
The relationship "played" between Teams and Players is similar to relationship "plays" between Teams and Players.

.
精选文档.
The information about children can be ascertained from motherOf and fatherOf relationships. Attribute ssNo is required since names are not unique.
.
精选文档.
.
精选文档.
a)
(b)
.
精选文档.
Assumptions
A Professor only works in at most one department.
A course has at most one TA.
A course is only taught by one professor and offered by one department.
Students and professors have been ass