Database
Management
System
Lecture - 8
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Database Management System Lecture 8: Keys and Relationships in ER Data Model, Slides of Introduction to Database Management Systems
A part of a database management system lecture series on docsity.com. It covers the concepts of keys, their different types including super keys, candidate keys, and primary keys, as well as the difference between simple and composite keys. The document also explains the need for keys and the concept of relationships in the er data model.
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2011/2012
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Database
Management
System
Lecture - 8
Today’s Overview
Key and its different types
Relationships in E-R Data
Model
Types of relationships
Example of Key
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4 S1038 Shoaib Baber Model Town BCS 3 S1015 Tahira Ejaz Wah Cantt MCS 2 S1018 Arif Mehmood Satellite Town BIT 4 S1025 Suhail Shah Garhi Shahoo BCS 6
Simple or Composite Key
A key consisting of single attribute is
called simple key, e.g., StudID, itemNo
A key consisting of more than one
attribute is known as composite key ,
like {Program_Code,Course_Code}
Super Key Definition same as of key For example, for EMPLOYEE and STUDENT entity types EmpID and StudID are the superkeys respectively.
Composite Key Example
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4 S1038 Shoaib Baber Model Town BCS 3 S1015 Tahira Ejaz Wah Cantt MCS 2 S1018 Arif Mehmood Satellite Town BIT 4 S1025 Suhail Shah Garhi Shahoo BCS 6
Super Keys
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4 S1038 Shoaib Baber Model Town BCS 3 S1015 Tahira Ejaz Wah Cantt MCS 2 S1018 Arif Mehmood Satellite Town BIT 4 S1025 Suhail Shah Garhi Shahoo BCS 6
Candidate Key A candidate key is the super key that does not contain extra attributes. It might have more than one attribute that uniquely identifies an entity. e.g {name, address}
CK Example
StdId StdName Address ClName CurSem
S1020 Suhail Dar Mareer Hassan MCS 4 S1038 Shoaib Baber Model Town BCS 3 S1015 Tahira Ejaz Wah Cantt MCS 2 S1018 Arif Mehmood Satellite Town BIT 4 S1025 Suhail Shah Garhi Shahoo BCS 6
Primary Key
A primary key is the main/chosen
candidate key from the possible
set of candidate keys that is most
suitable for entity identification.
Primary Key