Unit 11 : Extended Entity Relationship Model

Question 1

What is the common characteristics for data model?

Answer 1

1. Conceptual simplicity without compromising the semantic completeness of the database
2. Represent the real world as closely as possible
3. Representation of real-world transformations must comply with consistency and integrity characteristics of any data model

Question 2

What is data abstraction?

Answer 2

1. Ways of classifying data models

Question 3

What are the process of data abstraction?

Answer 3

1. Many processes begin at high level of abstraction and proceed to an ever increasing level of detail

Question 4

Who defined a framework for data modeling based on the degrees of data abstraction?

Answer 4

1. American National Standards Institute ( ANSI )
2. Standards Planning and Requirements Committe ( SPARC )

Question 5

List out the framework for data modeling based on degrees of data abstraction ( 3 )

Answer 5

1. External
2. Conceptual
3. Internal

Question 6

Who view the external model of the data environment?

Answer 6

1. End Users

Question 7

What does the external model requires?

Answer 7

1. The modeler subdivide set of requirements and constraints who functional modules that can be examined within the framework of their external models

Question 8

What is the advantages of the external model? ( 4 )

Answer 8

1. Easy to identify specific data required to support each business unit’s operations
2. Facilitates designer’s job by providing feedback about the model’s adequacy
3. Creation of external models helps to ensure security constraints in the database design
4. Simplifies application program development

Question 9

What does the conceptual model represent?

Answer 9

1. The global view of the entire database

Question 10

What is the representation of data in the conceptual model?

Answer 10

1. Representation of data as viewed by the entire organization

Question 11

What is the conceptual model mainly focued on?

Answer 11

1. The basis for indentification and high-level description for main data objects, avoiding details

Question 12

What is the most widely used conceptual model?

Answer 12

1. Entity Relationship Model

Question 13

What does the conceptual model provides?

Answer 13

1. A relatively easily understood macro level view of data environment

Question 14

How does the conceptual model is independent of both software and hardware? ( 3 )

Answer 14

1. Does not depend on the DBMS software used to implement the model
2. Does not depend on the hardware used in the implementation of the model
3. Changes in either hardware or DBMS software have no effect on the database design at the conceptual level

Question 15

What models is more technical than the conceptual model?

Answer 15

1. The internal model

Question 16

How does the Internal Model represents the diagram?

Answer 16

1. Representation of the database as “seen” by DBMS

• Represents the database from the perspective of DBMS
• Maps the conceptual model to the DBMS

Question 17

What depicts a specific representation of an internal model?

Answer 17

1. Internal Schema

Question 18

What model operates at lowest level of abstration? ( Mention the name and what it describe )

Answer 18

1. The Physical Model
2. Describing the way data are saved on storage media such as disks or tapes

Question 19

Is the physical model dependent on both software and hardware?

Answer 19

1. Yes

• It takes into account the particular requirements and limitations of the devices, such as storage capacities, access speeds, and memory.

Question 20

What is the requirement for database designers to implement database design at the physical model?

Answer 20

1. Requires that database designers have a detailed knowledge of the hardware and software used to implement database design

Question 21

What is Extended Entity Relationship model?

Answer 21

1. The result of adding more semantic constructs to original entity relationship model

• It is called EERD

Question 22

List out the key concepts in EER (

Answer 22

1. Supertypes and Subtype Relationship
2. Specialization and Generalization
3. Inheritance

Question 23

What type ( super / sub ) contains common characteristics?

Answer 23

1. Supertype

Question 24

What type ( super / sub ) contains unique characteristics of each entity subtype?

Answer 24

1. Subtypes

Question 25

What type ( super / sub ) is a generic entity type that is related to one or more entity subtypes?

Answer 25

1. Supertype

Question 26

What does specialization hierarchy depicts?

Answer 26

1. Arrangement of higher-level entity supertypes ( parent entities ) and lower-level entity subtypes ( child entities )

Question 27

How are relationships sometimes described in a specialization hierarchy?

Answer 27

1. "IS-A" relationship

Question 28

Can a subtype exist independently of its supertype?

Answer 28

1. No, a subtype can exist only within context of supertype and every subtype can have only one supertype to which it is directly related

Question 29

Can specialization hierarchies have multiple levels?

Answer 29

1. Yes, they can have many levels of supertype/subtype relationships.

Question 30

What is attribute inheritance in specialization hierarchies?

Answer 30

1. Attribute inheritance means that subtypes automatically inherit attributes from their supertype

Question 31

What is a subtype discriminator?

Answer 31

1. The attribute in supertype entity that determines to which entity subtype each supertype occurrence is related

Question 32

What is the default comparison condition for subtype discriminator ?

Answer 32

1. Equality Comparison

Question 33

What subtypes ( disjoint , overlapping ) is also known as non-overlapping subtypes?

Answer 33

1. Disjoint Subtypes

Question 34

What is a disjoint subtypes?

Answer 34

1. Subtypes that contain unique subset of supertype entity set

Question 35

What is a overlapping subtypes?

Answer 35

1. Subtypes that contain nonunique subsets of supertype entity set

Question 36

What does completeness contratint specifies?

Answer 36

1. Specifies whether each entity supertype occurrence must also be member of at least one subtype * Which can be partial or total

Question 37

What does specialization do?

Answer 37

1. It provides the top down process of identifying lower-level, more specific entity subtypes from higher-level entity supertype * It is based on grouping unique characteristics and relationships of the subtypes

Question 38

What does generalization do?

Answer 38

1. Provides botton-up process of identifying higher-level, more generic entity supertype from lower-level entity subtypes * It is based on grouping common characteristics and relationships of the subtypes

Question 39

What does inheritance enables?

Answer 39

1. Enables entity subtype to inherit attributes and relationships of supertype

Question 40

Do all entity subtypes inherit their primary key attribute from their supertype?

Answer 40

1. Yes, all entity subtypes inherit their primary key attribute from their supertype, ensuring uniqueness across the hierarchy.

Question 41

How is the relationship between a supertype and its subtype(s) depicted at the implementation level?

Answer 41

1. At the implementation level, the supertype and its subtype(s) maintain a 1:1 relationship in the specialization hierarchy.