DB Summary

[TOC]

DBMS Intro

DBMS	RDBMS
DBMS stores data as a file.	RDBMS stores data in tabular form.
Data elements need to be accessed individually.	Multiple data elements can be accessed at the same time.
No relationship between data.	Data is stored in the form of tables, which are related to each other.
Normalization is not present.	Normalization is present.
DBMS does not support a distributed database.	RDBMS supports a distributed database.
It stores data in either a navigational or hierarchical form.	It uses a tabular structure where the headers are the column names, and the rows contain corresponding values.
It deals with a small quantity of data.	It deals with a large amount of data.
Data redundancy is common in this model.	Keys and indexes do not allow Data redundancy.
It is used for small organizations and deals with small amounts of data.	It is used to handle a large amount of data.
Not all Codd rules are satisfied.	All 12 Codd rules are satisfied.
Security is less	More security measures are provided.
It supports a single user.	It supports multiple users.
Data fetching is slower for a large amount of data.	Data fetching is fast because of the relational approach.
The data in a DBMS is subject to low security levels with regard to data manipulation.	There exist multiple levels of data security in an RDBMS.
Low software and hardware necessities.	Higher software and hardware necessities.

Physical level. The lowest level of abstraction describes how the data are actually stored.
Logical level. The next-higher level of abstraction describes what data are stored in the database, and what relationships exist among those data.
View level. The highest level of abstraction describes only part of the entire database.