Major Stringer Lawrence

FATHER OF INDIAN ARMY

Major General Stringer Lawrance is the first Commander In Chief of India (1761)

-He is known as the ‘Father of Indian Army’

-Born in 6^th march 1697 at Hereford (England)

-He was an English Soldier

-He went to India to Command East India Company Troops

-He successfully foiled an attempt French surprise at Cuddalore (Tamilnadu), but subsequently was captured by French Cavalry Patrol at Arian company (Arian kuppam) while leading Forces advancing on Pondicherry and kept prisoner till the peace of Axi-la-chapelle3

-Died in London on 10th Jan 1775                                                     Major General Stringer Lawrance

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RDBMS and Relational Algebra

RDBMS and Relational Algebra

Concept of RDBMS

            A relational database consists of a collection of tables or relations. Relation is a mathematical tern for a table.  Each table represents a relationship among a set of values. Since a table is a collection of such relationships it is called as a relation. The figure below represents a STUDENT relation.

Adm No	Roll No	Year	Name	Batch	Father	Mother	Dist code
22002	1	2011	Jibin	BA	Babu	Seetha	D-01
22003	20	2000	Deepu	BCOM	Santhosh	Sandhya	D-09
22004	13	2008	Vipin	BBA	Rajan	Rejani	D-02
22005	14	2012	Vyshakh	BA	Kiran	Kalyani	D-03
22006	19	2004	Prajeesh	BSC	Jayan	Jayalalitha	D-07
22007	21	2009	Dipin	BSC	Prakash	Prajitha	D-06
22008	9	2008	Jijesh	BCOM	Mohan	Latha	D-04

Domain: A domain is a pool of values from which actual values appearing in a given column are drawn.  The year column in STUDENT relation can have any valid year as its domain.

Tuple:  The rows of a relation are generally referred to as tuples. Each row in the STUDENT relation represents the personal details of a particular student.

Attributes: The columns of a relation are called attributes.  RegNo, RollNo, Year, Name, Father, and Mother are attributes of the STUDENT relation.

Cardinality:  The number of rows or tuples in a relation is called cardinality of the relation. The relation STUDENT has seven tuples and hence the cardinality of STUDENT relation is 7.

Degree: The number of attributes in a relation determines the degree of a relation. The relation STUDENT has 8 columns or attributes and therefore the degree of STUDENT relation is 8

Keys

Primary key: A primary key is one of the candidate keys chosen to be the unique identifier for a table by the database designer. But a super key is a combination of a primary key with any other attribute or group of attributes.

  

Alternate key: The candidate key that is not the primary key is called alternate key. A single attribute or a set of attributes which is a candidate key in another table is called foreign key. Foreign key helps to maintain integrity of the database.

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