Information Management - 4

Question 1

Entity Relationship Model

Answer 1

• ER model is the basis of ER diagrm
• represents conceptual database viweed as endsuer
• Composed of: entities, relationship, attribute

Question 2

Entities

Answer 2

• refers to entity and not a single entity
• Corresponds to table and not row in relational environment
• In Chen and Crow’s diagram, entity name is writtten inside the rectangle
• Entity is noun with capital lettters

Question 3

Attribute

Answer 3

characteristics of an entity

Question 4

Chen notation

Answer 4

attribute is written in an oval conncted to entity

Question 5

Crow’s foot

Answer 5

attribute is within the attribute box below any rectangle

Question 6

Required attribute

Answer 6

must have a value

Question 7

Optional Attribute

Answer 7

may be left null

Question 8

Composite Identifier

Answer 8

primary key composed of one or more attribute

Question 9

Identifiers

Answer 9

one or more attributes that uniquely identify each entity instance

Question 10

Composite attribute

Answer 10

can be subdivided

Question 11

Simple attribute

Answer 11

cannot be subdivided

Question 12

Single-value attribute

Answer 12

can only have a single value

Question 13

Multivalued attribute

Answer 13

can have multiple values

Question 14

Derived Attribute

Answer 14

can be calculated from other attribute

Question 14

Relationship

Answer 14

• Association between entities
• Participants are entities that participate in a relationship
• Relationships between entities always operate in both directions
• Relationship can be classified as 1:M
• Relationship classification is difficult to establish if only one side of the relationship is known

Question 15

Connectivity

Answer 15

relationship classification

Question 16

Cardinality

Answer 16

minimum and maximum number of entitiy occurance

Question 17

existence dependence

Answer 17

Entity exists in database only when it is associated with another related entity occurrence

Question 18

Existence Indepencence

Answer 18

• entity can exist apart from one or more related entities
• sometimes known as strong entities

Question 19

Weak Relationship

Answer 19

Exists if PK of related entity does not contain PK component of parent entity

Question 20

Strong Relationship

Answer 20

Exists when PK of related entity contains PK component of parent entity

Question 21

Weak Entity

Answer 21

• existence-dependence
• primary key came from parent key

Question 22

Optional Participation

Answer 22

One entity occurrence does not require corresponding entity occurrence in particular relationship

Question 23

Mandatory Participation

Answer 23

One entity occurrence requires corresponding entity occurrence in particular relationship

Question 24

Relationship Degree

Answer 24

indicates the number of entities and participants associated with the relationship

• Unary Relationship - associated with a single entitity
• Binary Relationship - associated with two entities
• Ternary Relationship -associated with three entities

Question 25

Recursive Relationship

Answer 25

Relationship can exist between occurrences of the same entity set

Question 26

Assiciative (Compostite) Entity

Answer 26

• bridge the entities
• Implement M:N relationship
• Composed of pk of each entities
• may also contain additional attributes

Question 27

UML class diagrams

Answer 27

used to represent static data structures in data model