Dbms chapter vii
Upcoming SlideShare
Loading in...5
×
 

Dbms chapter vii

on

  • 39 views

join table

join table

Statistics

Views

Total Views
39
Views on SlideShare
39
Embed Views
0

Actions

Likes
0
Downloads
2
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Dbms chapter vii Dbms chapter vii Presentation Transcript

  • Subject Name Code Credit Hours Database System COMP 219 3 Chapter VII
  • 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.
  • 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}
  • 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
  • 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”.
  • 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
  • Subject Name Code Credit Hours Database System COMP 219 3 Relation schema • Empoyee(Employee_schema) denote that • Employee is a relation on Employee_schema
  • 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.
  • 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.
  • 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,
  • Subject Name Code Credit Hours Database System COMP 219 3 Keys • E.g.. eid Ename eaddr dno dnamedno dloc Employee pnamepno eid Dept Project
  • 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