Relational Model concept
Relational model can represent as a table with columns and rows. Each row is known as a tuple. Each table of the column has a name or attribute.
Domain: It contains a set of atomic values that an attribute can take.
Attribute: It contains the name of a column in a particular table. Each attribute Ai must have a domain, dom(Ai)
Relational instance: In the relational database system, the relational instance is represented by a finite set of tuples. Relation instances do not have duplicate tuples.
Relational schema: A relational schema contains the name of the relation and name of all columns or attributes.
Relational key: In the relational key, each row has one or more attributes. It can identify the row in the relation uniquely.
Example: STUDENT Relation
|
NAME |
ROLL_NO |
PHONE_NO |
ADDRESS |
AGE |
|
Ram |
14795 |
7305758992 |
Noida |
24 |
|
Shyam |
12839 |
9026288936 |
Delhi |
35 |
|
Laxman |
33289 |
8583287182 |
Gurugram |
20 |
|
Mahesh |
27857 |
7086819134 |
Ghaziabad |
27 |
|
Ganesh |
17282 |
9028 9i3988 |
Delhi |
40 |
- In the given table, NAME, ROLL_NO, PHONE_NO, ADDRESS, and AGE are the attributes.
- The instance of schema STUDENT has 5 tuples.
- t3 = <Laxman, 33289, 8583287182, Gurugram, 20>
Properties of Relations
- Name of the relation is distinct from all other relations.
- Each relation cell contains exactly one atomic (single) value
- Each attribute contains a distinct name
- Attribute domain has no significance
- tuple has no duplicate value
- Order of tuple can have a different sequence
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