Computer Notes On Database Management System

Notes On Database Management System

Database: A database contains a collection of related items or facts arranged in a specific structure.

DBMS: DBMS is the acronym of Data Base Management System. It is a collection of interrelated data and a set of programs to access this data in a convenient and efficient way. It controls the organization, storage, retrieval, security and integrity of data in a database.

The information contained in a database is represented on two levels:

1. Data (which is large and is being frequently modified)
2. Structure of data (which is small and stable in time)

Features of Database

Faithfulness: The design and implementation should be faithful to the requirements.

Avoid Redundancy: This value is important because redundancy.

Simplicity: Simplicity requires that the design and implementation avoid introducing more elements than are absolutely necessary.

Right kind of element: Attributes are easier to implement but entity sets are relationships are necessary to ensure that the right kind of element is introduced.

Types of Database:

Centralized Database: All data is located at a single site.

Distributed Database: The database is stored on several computer.

Users of a DBMS

Database Administrator (DBA): DBA takes care of the administrative tasks of DBMS as the name suggests and his major

responsibilities are given below.

Management of information

Liaison with users

Enforcing security and integrity rules

Database backup and recovery

Monitoring database performance

Database designers:

Person responsible for preparing external schemas for applications, identifying and integrating user needs into a conceptual (or community or enterprise) schema.

Application programmers:

Application programmers write programs to access/insert/update/delete data from/to database by making use of the various database components.

End users:

Users who query and update the database through fixed programs (invoked by non-programmer users) e.g., banking.

Advantages of a DBMS :

Data independence
Reduced data redundancy
Increased security
Better flexibility
Effective data sharing
Enforces integrity constraints
Enables backup and recovery

Most important term about database:

Fields:- Each piece of  information in the address book is stored in its own location called a field.

Records:- One full set of fields that is all the related information about one person or object is called a record.

Levels of Data Abstraction: There are three levels of data abstraction as given below

Physical Level: It is lowest level of abstraction and describes how the data are actually stored and complex low level data structures in detail.

Logical Level: It is the next higher level of abstraction and describes what data are stored and what relationships exist among those data. At the logical level, each such record is described by a type definition and the interrelationship of these record types is defined as well. Database administrators usually work at this level of abstraction.

View Level: It is the highest level of abstraction and describes only part of the entire database and hides the details of the logical level.

Working with a Database:

The DBMS interface presents the user with data and the tools required to work with the data.

Creating tables: The first step in building any database is to create one or more tables. As we know tables hold the raw data that the DBMS will work with.

Entering and editing data: It alllows you to create or edit a data entry form.

viewing data: The way data appears on screen contributes to how well users can work with it.

Querying the database: A query is a more powerful type of filter that can gather information from multiple tables in a relational database.

Sorting records: Sorting arranges records according to the contents of one or more fields.

Generating reports: A report is printed information that, like a query result, is assembled by gathering data based on user supplied criteria.

Difference between File system & DBMS

File System

File system is a collection of data. Any management with the file system, user has to write the procedures

File system gives the details of the data representation and Storage of data.

In File system storing and retrieving of data cannot be done efficiently.

Concurrent access to the data in the file system has many problems like reading the file while other deleting some information, updating some information

File system doesn’t provide crash recovery mechanism.eg. While we are entering some data into the file if System crashes then content of the file is lost.

Protecting a file under file system is very difficult.

DBMS

It  is a collection of data and user is not required to write the procedures for managing the database.

DBMS provides an abstract view of data that hides the details.

It is efficient to use since there are wide varieties of sophisticated techniques to store and retrieve the data.

It takes care of Concurrent access using some form of locking.

DBMS has crash recovery mechanism, DBMS protects user from the effects of system failures.

DBMS has a good protection mechanism.

Schema: A schema is also known as database schema. It is a logical design of the database and a database instance is a snapshot of the data in the database at a given instant of time. A relational schema consists of a list of attributes and their corresponding domains.

Types of Schemas: It can be classified into three parts, according to the levels of abstraction.

Physical/Internal Schema: Describes the database design at the physical level.

Logical/Conceptual Schema/Community User View: Describes the database design at the logical level.

Sub-schemas /View/External Schema: Describes different views of the database views may be queried combined in queries with base relations, used to define other views in general not updated freely.