Index Classification, Views - Database Management - Lecture Slides, Slides of Introduction to Database Management Systems

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Database

Management

System

Lecture - 39

Index Classification

 Clustered vs. unclustered :

 If order of data records is the same as order of index data entries, then called clustered index.

Clustered vs.

Unclustered Index

Index entries Dataentries

direct search for (Index File) (Data file) Data Records

data entries entries^ Data

Data Records

CLUSTERED UNCLUSTERED

When to Use Indexes

Useful on large tables

Required on PK

Useful for attributes appearing

in where, order by and group by

clauses

Indexes Summary

Useful tool to speedup the data access

Can be unique or non-unique

Can be implemented through different techniques

Be careful; they involve overhead

Views

Why Views?

Security

 Show the data to a users’ group that is necessary/required for them  Give only necessary authorizations  No concern with rest of the data

Why Views?

Efficiency

 Part of a query that is frequently used (a subquery), define it as a view  The view definition will be stored and will be executed anytime anywhere view is referred Docsity.com

Characteristics of Views

Not exactly the external views of 3-level schema architecture Major Types  Dynamic  Materialized  Partitioned  Simple/complex

Dynamic Views

Data is not stored for the views

Definition is stored in the

schema

Executed every time view is

referred

Database

Management

System

Lecture - 39