The document discusses key concepts of the relational database model including its basic structure using tables and relations. It describes how relations are represented by schemas and instances. It defines the different types of keys like primary keys, foreign keys, and composite keys. It also introduces relational algebra and calculus as procedural and non-procedural query languages for retrieving data in a relational database.

1. Subject Name Code Credit Hours
Database System COMP 219 3
Chapter VII

2. Subject Name Code Credit Hours
Database System COMP 219 3
Relational Model:
• It uses a collection of tables to represent
both data and relationships among those
data.
Basic Structure
 In this model each table is called as
relation. Each relation has a no. of
row is called tuples and columns
called as fields or attributes.

3. Subject Name Code Credit Hours
Database System COMP 219 3
Relational Model:
• For an attribute, a range of permitted values
can be specified. That range is called as
Domain of that attribute.
• E.g.. Age – attribute
• Domain (Age) = {1,2…100}

4. Subject Name Code Credit Hours
Database System COMP 219 3
Relational Model:
• A table of n attributes must be a subset of
D1*D2*…….Dn
• E.g..
Eid Ename Eaddr
1
2
3
Aaa
Bbb
ccc
South street
West street
New
Employee Relation

5. Subject Name Code Credit Hours
Database System COMP 219 3
Relational Model:
• To denote the value of attribute ‘a’ on second
tuple, then it can be denoted as t2[a]=value.
• E.g..
• t2[ename]=“bbb”.

6. Subject Name Code Credit Hours
Database System COMP 219 3
Relation schema
• It is the description about the structure of the
relation and the relation instance is the
snapshot of data in the relation at a given
instant in time.
• E.g.. Employee_schema=(eid,ename,eaddr)
Name of the schema

7. Subject Name Code Credit Hours
Database System COMP 219 3
Relation schema
• Empoyee(Employee_schema) denote that
• Employee is a relation on Employee_schema

8. Subject Name Code Credit Hours
Database System COMP 219 3
Keys
• Strong Entity set:
• The Primary key of the entity set becomes the primary
key of the relation.
• Weak Entity Set:
• The table corresponding a weak entity set includes
• the attributes of the weak entity set &
• primary key of the strong entity set on which the weak
entity set depends.

9. Subject Name Code Credit Hours
Database System COMP 219 3
Keys
Relationship Set:
The union of the primary key of the related entity sets
becomes a super key of the relation.
Combined Tables:
If there exists many to one relationship set from A to B,
then the prim.key of A becomes the prim.key of the
relation & the relation consists of the attribues of A and
attributes of the relationship set.

10. Subject Name Code Credit Hours
Database System COMP 219 3
Keys
Foreign Key:
An attribute of a relation r1 that references
relation r2 is called as foreign key attribute.
Schema Diagram:
A relation schema can be depicted pictorially
by schema diagram,

11. Subject Name Code Credit Hours
Database System COMP 219 3
Keys
• E.g..
eid Ename eaddr dno
dnamedno dloc
Employee
pnamepno eid
Dept
Project

12. Subject Name Code Credit Hours
Database System COMP 219 3
Query Languages:
• It is a lang in which a user requests
information from db.
Query Languages
Procedural Language Non Procedural Language
Specifies what data are required &
specify how to get those data e.g
Relational Algebra
Specifies what data are required without
specify how to get those data e.g.
Relational calculus