prelim lesson2

Question 1

DBMS is the only entity where user directly sits
on DBMS and uses it. Any changes done here
will directly be done on DBMS itself. It does
not provide handy tools for end users and
preferably database designer and
programmers use single tier architecture.

Answer 1

1tier

Question 2

• DBMS is 2-tier then must have some application,
  which uses the DBMS

. Programmers use ____ architecture where they access DBMS by means of
application. Here application tier is entirely
independent of database in term of operation, design
and programming.

Answer 2

2tier

Question 3

Most widely used architecture

Answer 3

3tier

Question 4

tells how the logical structure of a database is modeled.
Data Models are fundamental entities to introduce abstraction in
DBMS. Data models define how data is connected to each other and
how it will be processed and stored inside the system.

Answer 4

Data model

Question 5

• precise description of the data
  content in a system.
• Underlying structure of a
  database.
• Conceptual tool.
• Data + Relationship +
  Semantics + Constraints
• Design the database at physical,
  logical and view level
• The data modelling or data structuring
  represents the nature of data, and the business
  logic to control the data. It is also organize the
  database.
• The structure of data are explicitly determines
  by the data model.
• Data model helps to communicate between
  business people, who requires the computer
  system, and the technical people who can fulfill
  their requirements.

Answer 5

Data modeling

Question 6

Why do we create data models

Answer 6

• To aid in the development of a sound
  database design that does not allow
  anomalies or inconsistencies
• Goal: to create database tables that do not
  contain duplicate data values that can
  become inconsistent

Question 7

a class of real world objects having
common attributes (e.g., sites, variables,
methods).

Answer 7

Entity

Question 8

A characteristic or property of an
entity (site name, latitude, longitude)

Answer 8

Attribute

Question 9

an association between two or
more entities

Answer 9

relationship

Question 10

the number of entities on either
end of a relationship (one-to-one, one-to many, many-to-many, etc.)

Answer 10

Cardinality

Question 11

An entity in ER model is real world entity, which
has some properties called attributes. Every attribute is
defined by its set of values called domain.

Answer 11

Entity

Question 12

The logical association among entities is
called relationship. Relationships are mapped with
entities in various ways. Mapping cardinalities define
the number of association between two entities.

Answer 12

Relationship

Question 13

Relationship types

Answer 13

• One to one
• One to Many
• Many to one
• Many to Many

Question 14

are represented by means of
rectangles. Rectangles are named with the
entity set they represent.

Answer 14

Entity

Question 15

______ are the properties of entities.
_____ are represented by means of ellipses.
Every ellipse represents one attribute and is
directly connected to its entity (rectangle).

Answer 15

Attributes

Question 16

If the attributes are _____, they are further
divided in a tree like structure. Every node is then
connected to its attribute. That is, composite
attributes are represented by ellipses that are
connected with an ellipse.

Answer 16

Composite Attributes

Question 17

attributes are depicted by dashed
ellipse

Answer 17

Derived

Question 18

attributes are depicted by double
ellipse.

Answer 18

Multivalued

Question 19

T-A

____ attributes are atomic values,
which cannot be divided further. For example, a
student’s phone number is an atomic value of 10 digits.

Answer 19

Simple attribute

Question 20

T-A
are made
of more than one simple attribute. For example, a
student’s complete name may have first_name and
last_name.

Answer 20

Composite Attribute

Question 21

T-A
are the
attributes that do not exist in the physical database, but
their values are derived from other attributes present in
the database. For example, average_salary in a
department should not be saved directly in the
database, instead it can be derived. For another
example, age can be derived from data_of_birth.

Answer 21

Derived attribute

Question 22

T-A
attributes contain
single value. For example − Social_Security_Number.

Answer 22

Single-value attribute

Question 23

T-A
may
contain more than one values. For example, a person
can have more than one phone number, email_address,
etc.

Answer 23

Multi-value attribute

Question 24

Entity set and keys

A set of attributes (one or
more) that collectively identifies an entity in
an entity set.

is a group of single or multiple
keys which identifies rows in a table. A Super
key may have additional attributes that are
not needed for unique identification.

Answer 24

Super key

Question 25

Entity set and keys

A minimal super key is
called a candidate key. An entity set may
have more than one candidate key.

is a set of attributes that
uniquely identify tuples in a table. Candidate
Key is a super key with no repeated attributes.
The Primary key should be selected from the
candidate keys. Every table must have at least
a single candidate key. A table can have
multiple candidate keys but only a single
primary key.

Answer 25

Candidate key

Question 26

Entity-set and keys

is one of the
candidate keys chosen by the database
designer to uniquely identify the entity set.

is a column or group of columns in a table that uniquely identify
every row in that table. The Primary Key can’t be a duplicate meaning the same
value can’t appear more than once in the table. A table cannot have more than
one primary key.

Answer 26

Primary

Question 27

defines the number of entities in one
entity set, which can be associated with the
number of entities of other set via relationship set.

Answer 27

Cardinality

Question 28

One entity from entity set A can be
associated with at most one entity of entity set B
and vice versa.

Answer 28

One-to-one

Question 29

One entity from entity set A can
be associated with more than one entities of
entity set B however an entity from entity set B,
can be associated with at most one entity

Answer 29

One-to-many

Question 30

More than one entities from
entity set A can be associated with at most one
entity of entity set B, however an entity from
entity set B can be associated with more than
one entity from entity set A

Answer 30

Many-to-one

Question 31

One entity from A can be
associated with more than one entity from B
and vice versa.

Answer 31

Many-to-many

Question 32

has the power of expressing
database entities in a conceptual hierarchical
manner. As the hierarchy goes up, it generalizes
the view of entities, and as we go deep in the
hierarchy, it gives us the detail of every entity
included

Answer 32

ER model

Question 33

Two types of ER model

Answer 33

Generalization
Specialization

Question 34

the process of generalizing entities, where the generalized
entities contain the properties of all the generalized entities, is
called generalization. In generalization, a number of entities
are brought together into one generalized entity based on
their similar characteristics. For example, pigeon, house
sparrow, crow and dove can all be generalized as Birds

Answer 34

Generalization

Question 35

, a group of entities is
divided into sub-groups based on their
characteristics. Take a group ‘Person’ for
example. A person has name, date of
birth, gender, etc. These properties are
common in all persons, human beings.
But in a company, persons can be
identified as employee, employer,
customer, or vendor, based on what role
they play in the company.

Answer 35

Specialization

Question 36

Inheritance is an important
feature of Generalization and
Specialization. It allows lowerlevel entities to inherit the
attributes of higher-level entities.

Answer 36

Inheritance

Question 37

Every relation has some conditions that must hold for it to be a valid relation. These
conditions are called R____ I_____ C_____

Answer 37

Constraints

Question 38

Three main integrity constraints

Answer 38

Key constraints
Domain constraints
Referential integrity constraints

Question 39

There must be at least one minimal subset of
attributes in the relation, which can identify a tuple
uniquely. This minimal subset of attributes is
called key for that relation. If there are more than
one such minimal subsets, these are
called candidate keys.
* Key constraints force that −
* in a relation with a key attribute, no two
tuples can have identical values for key
attributes.
* a key attribute can not have NULL values.

Answer 39

Key constraints

Question 40

is a key used to link two tables together

is a field (or collection of fields) in one table that
refers to the PRIMARY KEY in another table.

Answer 40

Foreign key