Database Management System

  • Database management system is a software which is used to manage the database. For example: MySQLOracle, etc are a very popular commercial database which is used in different applications.
  • DBMS provides an interface to perform various operations like database creation, storing data in it, updating data, creating a table in the database and a lot more.
  • It provides protection and security to the database. In the case of multiple users, it also maintains data consistency.

DBMS allows users the following tasks:

  • Data Definition: It is used for creation, modification, and removal of definition that defines the organization of data in the database.
  • Data Updation: It is used for the insertion, modification, and deletion of the actual data in the database.
  • Data Retrieval: It is used to retrieve the data from the database which can be used by applications for various purposes.
  • User Administration: It is used for registering and monitoring users, maintain data integrity, enforcing data security, dealing with concurrency control, monitoring performance and recovering information corrupted by unexpected failure.
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Schema and Instance in DBMS

 12 Apr  Admin

Schema 

schema is the complete design of database it is also known as intension. It is the collection of named objects.

Design of a database is called the schema. Schema is of three types: Physical schema, logical schema and view schema.

The database system has various schemata separated according to the levels of abstraction :-

  1. The physical schema is the lowest level of a schema which describes how the data stored on the disk or the physical storage.
  2. The logical schema is the intermediate level of a schema which describes the structure of the database to the database designers. It also specifies what relationship exists between the data.
  3. The external schema or subschema is the highest level of a schema which defines the views for the end users.

Instance

An instance is the information collected in a database at some specific moment, and it is also known as state or extension. It is a snapshot where the current state or occurrence of a database is framed at that moment.

The data stored in database at a particular moment of time is called instance of database. Database schema defines the variable declarations in tables that belong to a particular database; the value of these variables at a moment of time is called the instance of that database.

Schema and instance are somehow related, a schema is the initial state of the database where the database is designed at first. On the other hand, an instance is a state when data is loaded into the database or when any change is acquired by the corresponding database. Schema is the detailed description of the structure of database whereas the information stored at a specific moment in a database is known as an instance.

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Data Abstraction in DBMS

 03 Sep  Admin

Abstraction,in general, is the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics.Database systems are made-up of complex data structures. To ease the user interaction with database, the developers hide internal irrelevant details from users. This process of hiding irrelevant details from user is called data abstraction.

There are mainly levels of data abstraction:

Physical level: Physical level is the lowest level of data abstraction which describes how data is actually stored in database. You can get the complex data structure details at this level.

Logical level: Logical level is the middle level of 3-level data abstraction architecture which describes what data is stored in database.

View level: Highest level of data abstraction is view level which describes the user interaction with database system.

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Levels of DBMS Architecture

 03 Sep  Admin

This architecture has three levels:

1. External level  :-

    External level is also called view level. The reason this level is called “view” is because several users can view their desired data from this level which is internally fetched from database with the help of conceptual and internal level mapping. External level is the “ top level ” of the Level of DBMS Architecture.

Facts about External level:

  1. An external level is only related to the data which is viewed by specific end users.
  2. This level includes some external schemas.
  3. External schema level is nearest to the user
  4. The external schema describes the segment of the database which is needed for a certain user group and hides the remaining details from the database from the specific user group

2. Conceptual level  :-

      Conceptual level is also called logical level .The whole design of the database such as relationship among data, schema of data etc. are described in this level. It is maintained by DBA.

Facts about Conceptual level:

  1. Defines all database entities, their attributes, and their relationships
  2. Security and integrity information
  3. In the conceptual level, the data available to a user must be contained in or derivable from the physical level

3. Internal level  :-

       Internal level is also known as physical level. This level describes how the data is actually stored in the storage devices. It is responsible for storage allocation. This is the lowest level of the architecture.

Facts about Internal level:

  1. The internal schema is the lowest level of data abstraction
  2. It helps you to keeps information about the actual representation of the entire database. Like the actual storage of the data on the disk in the form of records
  3. The internal view tells us what data is stored in the database and how
  4. It never deals with the physical devices. Instead, internal schema views a physical device as a collection of physical pages.
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Views of data

 03 Sep  Admin

Different Views of Database

There are three different views of the database. The views are seen through the schema and the sub-schema of the data.

Logical view of the user of data

          This is a view of the application programmer or user as he wants it. This could be a partial view of the database. For example, the quality control manager and the purchase manager would view the data differently for their use.

The view of database administrator (DBA)

           This is a view of the person who is managing the database through the creation, updating, structuring and ensuring that it is up-to-date. The view of the DBA is a global view.

Physical View

            This is the view of the data actually stored and organized on the physical devices.

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