Computer (Computer Notes on Database Management System)

Computer 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 Database 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:

• Data (which is large and is being frequently modified)
• 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.

Tables:- A complete colleciton of records makes a table.

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.

          View Level …Defined by User 

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.

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 allows 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.                           

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.