Chapter 3

Question 1

define entities

Answer 1

specific things or objects described by database

Question 2

define attributes

Answer 2

properties used to describe an entity

Question 3

what are the 2 types of attributes?

Answer 3

Simple = attribute has a single value
composite = attribute composed of multiple attributes

Question 4

what is a multi-valued attribute?

Answer 4

attribute that has multiple attributes

i.e a car can be red and black at the same time

Question 5

define entity type

Answer 5

entities with the same basic attributes like a java class

Question 6

define key attribute

Answer 6

attribute that distinguishes multiple entities of the same entity type

• Can be composite

Question 7

define entity set

Answer 7

current state of all entities of an entity type

Question 8

define value set

Answer 8

set of values associated with an attribute

Question 9

define relationship

Answer 9

relates 2 or more distinct entities with a specific meaning

• degree of relationship is the number of participating entities

Question 10

what are the 3 cardinality ratios?

Answer 10

specifies maximum participation

• 1 to 1
• 1 to many
• many to many

Question 11

what are the 2 existence dependency constraints?

Answer 11

specifies minimum participation?

• zero (optional participation, existence-dependent)
• one or more (mandatory)

Question 12

define weak entity type

Answer 12

entity that doesn’t have a key attribute and is dependent on another entity type for identification

Question 13

define partial key

Answer 13

key attribute when combined another key attribute)

Question 14

what are sub/super classes in enhanced ERDs?

Answer 14

• subclasses function just like java where subclasses inherit attributes of superclass (is a special case of a superclass)
• superclasses are general cases of subclasses, also like java

Question 15

What are the 3 basic constraints of specializations

Answer 15

1. Membership
2. Disjointness
3. Completeness

Question 16

How can membership constraints be defined?

Answer 16

predicate/condition-defined: based on some condition
attribute defined: all subclasses have their membership condition on the same attribute
user defined: no condition so membership is specified by the user on an entity-to-entity basis

Question 17

How can disjointness constraints be defined?

Answer 17

• entities of subclasses of the same superclass are mutually exclusive
• indicated by d

Question 18

How can overlapping constraints be defined?

Answer 18

• entities of subclasses of the same superclass can overlap
• indicated by o

Question 19

What is the total completeness constraint?

Answer 19

Every entity of the superclass must belong to some subclass
indicated with double lines in eer

Question 20

What is the partial completeness constraint?

Answer 20

an entity may not belong to any subclass
indicated with single line in eer