basic database terms

8/13/2019 Basic Database Terms

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Basic Database Terms


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• FIELD/COLUMN: represents one related part of a table

and is the smallest logical structure of storage in the

database.

• RECORD/ROW: collection of multiple related fields that

can be treated as a unit.

• TABLE: collection of logically related multiple records.

• DATA TYPE: determines the type of data that can bestored in a column.

• KEY: column value in a table that is used to either

uniquely identify a row of data in a table, or establish a

relationship with another table.

– Primary Key

– Foreign Key

– Candidate Key


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Primary Key

• Denotes a key that is chosen by the database designer

as the principal means of identifying unique records

within a table.

• For example, the employee’s code field can be

designated as the primary key because all employee

codes are unique and the value once entered is never

changed until the person is in the organization.


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Foreign Key

• It is the combination of one or more columns in a table(parent table) that references a primary key in another

table (child table).

Purchase_ID Purchase_DATE ITEM_CODE

ITEM_CODE ITEM_COST ITEM_QUANTITY

Foreign Key

Primary Key

Primary Key

ITEM

PURCHASE


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Candidate Key

• A combination of one or more fields whose value

uniquely identifies a record in a table, i.e., no two records

in a table can have the same key value.

• Every key field is a candidate key but there cannot be

more than one primary key in a table.


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Logical Data Concepts

• Entity: an object that has its existence in the real world.• Attribute: units that describe the characteristics or

properties of entities.

• Relationship: an association, dependency or link

between two or more entities.

CUSTOMER GOODSGoods

Bough

t

Code

Name

Address Code Price


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Components of a DBMS

• Users: – Application Programmers

– End Users

– DBA

• Software: – DBMS

– Operating System

– Network Software (if necessary)

– Application Programs

• Hardware: – Storage and input & output devices

• Data


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PhysicalDatabase

Transaction Manager

Recovery Manager

DBMSUser

Interface

DataManager

FileManager

DiskManager

User requestRequest for

specific record

Request for

specific blockInput/Output

DBMS Components


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Database Administrator

• Custodian of database accuracy, efficiency, maintenance,

and development.

• Responsibilities:

– Granting different types of authorization to regulate which parts of

the database various users can access.

– Ensuring regular backups of a database and in case of failure,suitable recovery procedures are used to restore the database

services with as little down time as possible.

– Ensuring regular and accurate update of database.

– Collaborating in the design and development of databases to

meet new user needs and respond to anticipate technologicalinnovations.

– Identifying and resolving user’s problems.

– Communicating regularly with internal technical applications and

operational staff to ensure the database integrity and security.


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Database Languages

• Data Definition Language (DDL): used to create

database and its objects. Used by the DBA during the

building and removal phases of a database project.

• Data Manipulation Language (DML): used to retrieve,

insert, modify and delete database information. Used by

all database users during the routine operation of the

database.


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Normalisation

• It is the process of reducing data redundancy in a

relational database.

• Fundamental Principle: the same data should not be

stored in multiple places.

• Types of Normalisation:

– 1NF

– 2NF

– 3NF


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First Normal Form (1NF)

STUDENTS Table-

STUDENT_ID STUDENT_NAME SUBJECT_1 SUBJECT_2

STUDENTS Table-

SUBJECTS Table-

STUDENT_ID STUDENT_NAME

GRADESTUDENT_ID SUBJECT_NAME

So, A table is in 1st Normal Form if it contains no repeating

groups, i.e., no two fields stores the same kind of information in

a single table.


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Second Normal Form (2NF)

• Depends on the concepts of the primary key and

functional dependency.

• A database is said to be in 2NF if it is in 1NF and every

attribute is fully functionally dependent on the primary

key.

• Thus, the relation is in 1NF with no repeating groups,

and all non-key attributes must depend on the whole

key, not just some part of it.


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Third Normal Form (3NF)

• A table is said to be in 3NF if all the non-key fields are

independent, i.e., no two non-key fields of the table

depend on each other.

• 3NF seeks to eliminate all attributes from a table that are

not directly dependent upon the primary key.

PROJECT_ID MANAGER ADDRESS

P1 Vivek Gamma

P2 Vikas Delta

P3 Vivek Gamma

P4 Vivek Gamma

Projects Table PROJECT_ID MANAGER

P1 Vivek

P2 Vikas

P3 Vivek

P4 Vivek

Projects Table

MANAGER ADDRESS

Vivek Gamma

Vikas Delta

MANAGERS Table

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