CH 5 - ER Modelling

Question 1

What is the definition of a model according to Webster’s Dictionary?

Answer 1

A model is a “description or analogy used to visualize something that cannot be directly observed.”

Question 2

What is a data model?

Answer 2

A data model is a relatively simple representation of complex real-world data structures.

Question 3

what are the degrees of abstraction

Answer 3

-conceptual
-internal
-external
-physical

Question 4

What does the conceptual model in data modeling represent?

Answer 4

It provides a global view of data,

serves as the basis for identifying and describing main data items,

and is typically represented using an ERD (Entity-Relationship Diagram). It is hardware and software independent.

Question 5

What is the internal model in data modeling?

Answer 5

The internal model represents the database as seen by the DBMS, adapts the conceptual model to a specific DBMS, and is software dependent.

Question 6

What is the external model in data modeling?

Answer 6

The external model represents users’ views of the data environment, provides subsets of the internal view, and ensures the adequacy and security of the conceptual model.

Question 7

What does the physical model in data modeling represent?

Answer 7

The physical model is the lowest level of abstraction and is software and hardware dependent. It requires the definition of physical storage devices and access methods.

Question 8

What does the Entity-Relationship (E-R) Model represent?

Answer 8

-conceptual view of the database
-showing the main components like entities and attributes and relationships

Question 9

In the E-R Model, what is an entity?

Answer 9

An entity corresponds to an entire table (not a row) and is represented by a rectangle in an ERD.

Question 10

What are attributes in the E-R Model?

Answer 10

Attributes are characteristics of entities and relationship

Their domain is the set of possible values they can have.
Primary keys are underlined.

Question 11

er attributes

Answer 11

simple
composite
single valued
multi valued
derived

Question 12

What is a simple attribute?

Answer 12

an attribute that cannot be subdivided, such as age, sex, or marital status.

Question 13

What is a composite attribute?

Answer 13

A composite attribute can be subdivided into additional attributes, like an address can be divided into street, city, and zip code.

Question 14

What is a single-valued attribute?

Answer 14

it can have only one value, such as a person having one social security number.

Question 15

What is a multi-valued attribute?

Answer 15

A multi-valued attribute can have many values, such as a person having several college degrees.

Question 16

What is a derived attribute?

Answer 16

A derived attribute can be calculated using an algorithm, like age being derived from the date of birth.

Question 17

What is a relationship in the E-R Model?

Answer 17

A relationship is an association between entities, where connected entities are called participants.

Relationships operate in both directions and are described by connectivity (e.g., 1:1, 1:M)

cardinality.Expresses number of entity occurrences associated with one occurrence of related entity

Question 18

relational strengths

Answer 18

existence dependence. Entity’s existence depends on existence of related entities. Existence-independent entities can exist apart from related entities

weak(non - identifying). One entity is existence-independent on another. PK of related entity doesn’t contain PK component of parent entity

strong (identifying).One entity is existence-dependent on another. PK of related entity contains PK component of parent entity

Question 19

What is optional relationship participation?

Answer 19

Entity occurrence does not require a corresponding occurrence in related entity

Shown by drawing a small circle on side of optional entity on ERD

Question 20

What is mandatory relationship participation?

Answer 20

Entity occurrence requires corresponding occurrence in related entity

If no optionality symbol is shown on ERD, it is mandatory

Question 21

What is a weak entity?

Answer 21

A weak entity is one that is existence-dependent on another entity .

has a primary key that is partially or totally derived from the parent entity.

Question 22

What is relationship degree in the E-R Model? nb draw them

Answer 22

indicates the number of associated entities e.g

unary (single entity associated),

binary (two entities),

ternary (three entities).

Question 23

What are composite entities in the E-R Model?

Answer 23

are used to bridge M:N relationships

and are composed of primary keys of each entity needing connection.

Question 24

What is an entity supertype and subtype? nb draw them

Answer 24

its a generalization hierarchy whereby :

An entity supertype is a higher-level entity that has shared attributes,

while subtypes are lower-level entities with unique attributes.

Relationships can be disjoint (non-overlapping ‘G’) or overlapping ‘Gs’ , indicated by specific symbols in ERDs.

Question 25

What are the Chen and Crow’s Foot notations?

Answer 25

Chen notation was instrumental in moving conceptual design into practical database design,

while Crow’s Foot notation cannot detail all cardinalities but is widely used for simplicity in ERDs.

Question 26

what is Rein85 and IDEF1X

Answer 26

Rein85 is similar to crows foot and operates at higher level of abstraction.

while

IDEF1X uses fewer symbols and is a derivative of ICAM