Data Models

Question 1

Data model

Answer 1

Different levels of complexity/detail will be specified in the
conceptual & logical models, for schemas, and the
physical models

Question 2

Entities

Answer 2

anything about which data are to
be collected and stored - each instance is unique and distanct

nouns (ex: teacher, student)

Question 3

Attribute

Answer 3

characteristic of an entity

organized as columns in a table that is
about the entity and describes the entity

Question 4

Relationship

Answer 4

association among entities

Between any two entities there is some type of
relationship (it could be “none”).

Question 5

Types of relationships

Answer 5

one-to-one, one-to-many, many-to-many

Question 6

One-to-one relationship

Answer 6

each record in Table1 is related to one record in Table2; each record in Table2
is related to one record in Table1

Question 7

One-to-many relationship

Answer 7

each record in Table1 may be related to several records in Table2. Each
record in Table2 is related to one record in Table1

Question 8

Many-to-many relationship

Answer 8

each record in Table1 may be
related to several records in Table2, and each record in Table2 may be
related to several records in Table1

Question 9

How are relationships formed?

Answer 9

through common attributes

Question 10

key attributes

Answer 10

primary key & forgein key

Question 11

primary key

Answer 11

attribute (or combination of attributes) that
uniquely identifies any given row

each table must have this type of attribute

Question 12

forgein key

Answer 12

attribute whose
values match the primary key values in a
related table

Question 13

True or False: It is harder to achieve logical data independence than physical data independence

Answer 13

True

Question 14

Constraint

Answer 14

restriction placed on the data

this helps ensure data integrity

Question 15

Data Model Types

Answer 15

hierarchical (parent-child), network, entity-relational

Question 16

hierarchical (parent-child)

Answer 16

This model organizes data in a tree-like structure, where each record has a single parent, and each parent can have multiple child records. This creates a strict hierarchy

Pros: Simple, fast, and efficient for hierarchical data.

Cons: Lack of flexibility, as each child can have only one parent, making it difficult to model more complex relationships.

Question 17

network

Answer 17

The network model is more flexible than the hierarchical model. It uses a graph-like structure where entities are represented as nodes, and the relationships between them are shown as arcs or links. Unlike the hierarchical model, an entity can have multiple parents and multiple children.

pros: Flexible and supports complex relationships like many-to-many.

cons: More complicated to implement and manage than hierarchical models.

Question 18

entity-relational

Answer 18

The ER model is a conceptual and high-level model for representing data. It uses entities (objects or things) and relationships between them. Entities are connected by relationships, and each relationship can have attributes.

Pros: Conceptual and flexible, useful for designing databases, and easy to visualize with ER diagrams.

Cons: It’s abstract and doesn’t describe how data is physically stored.

Question 19

data modeling steps

Answer 19

1. Business rules, use cases (human-readable description of data)
2. Conceptual model (global view of entire DB w/entities, relationships, and constraints)
3. Logical Model (ER diagram)

Question 20

Differences between all data models?

Answer 20

• hierarchy = rigid
• network = flexible & allows M-M relationships
• er = abstract & conceptual