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Database Managment Systems

What is Database?

A database is a group of concern data which shows some facts of the real world. It is designed to populated and built with data for specific task.
The main function of Database to store, retrieve and manage to operate large amount of data. There are many databases available to handle data are: -

1. MySQL
2. mongoDB
3. SQL Server
4. Sybase
5. Oracle
6. Firebase

Relational Database

A relational database is kind of database that provides the authentication to data points that are associated to one another data. It is based upon relational model. There are two main technologies used in relational database are Schema and Instance.

Schema: schema concern with structure like name of relation, types of each name and table.

Instance: It is table with name of column and row.

Each row in the table is an associated with a unique ID known as the key.

Relational Database Properties

1. Atomicity
2. Query processing
3. Unique
4. Concurrency
5. Consistency
6. Integrity
7. Durability

Cloud Database

It is collection of data which is either unstructured or structured that kept on public or private infrastructure platform is called as Cloud Computing. Cloud data are accessible over internet only.

Some cloud examples

1. Microsoft SQL Server
2. Amazon Web Services (AWS)
3. Oracle Database Cloud services
4. SAP
5. EnterpriseDB
6. Rackspace

NoSQL Database

NoSQL database is non-relational Database management systems which avoid joins and need not required constant schema and easy to scale. It is generally used for real web application and large amount of data to be stored. NoSQL stands for “Not Only SQL”. Some of the companies using NoSQL Database are Facebook, Twitter, Google etc. to store hug amount of Data.

Advantage of NoSQL Database

1. It Is highly scalable
2. It is Highly Available

Disadvantage of NoSQL Database

1. Backup is one of challenging task of NoSQL Database.
2. GUI tools are not easily available on market for NoSQL Database.
3. It is open-source Database so there is no reliability yet decided.

Database Management System

1. DBMS is a software by which database is managed. Some of the DBMS are MySQL, Oracle, SQL Server etc are a very popular commercial database which is used in various applications.
2. DBMS provides an interface to perform different operations like storing data, database creation, updating data, creating a table in the database.
3. It gives security and protection to the database. Consistency is always in case of multiple users also.

Characteristics of DBMS

1. It stores any kind of data which is available in real world.
2. Data Integrity is one of important characteristics of DBMS. It ensures the Reliability and quality of the database.
3. Recovery and backup of data is one of characteristics of DBMS. This type of characteristics must be in all database so that there is no chance of loss of Data.
4. It has ACID properties.
5. It can decrease the complex relation between data.
6. DBMS has consistency.

Entity-Relationship Model (ER Diagram)

It is high level conceptual data model diagram. Entity Relationship Model is blueprint or design of database which is implemented later as a database. ER diagram provides relationship among the entity database.

Entity-Relationship model based on the following:

1. Relationship among the entities.
2. Entities and their attributes.

The above is explained here:

Relationship: It is context of database which exits between two relational database tables in which primary key has reference of foreign key of table of another table. It allows database to divide and store data in various tables while attaching the disparate items data.

Mapping cardinalities explain the number of attached between two entities.

Mapping cardinality:

1. One to one
2. One to many
3. Many to many
4. Many to one

Entity:It is set of collection of same kinds of entities. In the real-world object, entity can be exits either aminate or not animate which is simply detectable.

Attributes

Table organises data in column and row in Relational Database Management systems in which row are called as records and column as called attributes. All attributes have values. Attribute explain the instance of row in database.

Data Model schema and Instance

A schema diagram can show some characteristics of a schema like the data type, name of record type, and constraints.

1. When data stored in database at certain time is known as an instance of database.
2. The whole design of database is known as schema.
3. By the help if Visual diagram, A database schema can be shown. Visual diagram represents the database objects and relationship with each other.
4. It is Skelton structure of Database. It shows the logical value of the whole database.
5. A schema has schema objects like Primary key, views, data types, column, table, foreign key etc.

Data Independence

1. It is defined by the three-schema architecture.
2. It refers characteristic of being able to changes the schema at one level of the database system without affecting the schema at the next upper level.

There are two types of data independence:

1. 1. Logical data Independence
2. 2. Physical Data Independence

Logical Data Independence: It is referring properties of able to modify the conceptual schema without having alter in external schema. There are no changes in users view of data if we can do changes in conceptual view of data. At user’s interface level the Logical Data Independence has been occurs.

Physical Data Independence: It always occurs at logical interface level. It is used to divide the conceptual levels from internal levels. It has explained as ability to modify in internal schema without having alter in conceptual schema.

DBMS Transaction Management: ACID Properties

What is a Database Transaction?

It is a logical unit of processing in a Database Management System which involve one or more database access operation. The Database transaction shows real-world events of any enterprise in nutshell.

Why do we need concurrency in Transactions?

The shared resource is accessed by Database. It is used by many users and processes concurrently. For example, In Railway, and air reservations systems, supermarket inventory, stock market monitoring, the banking system and checkouts, etc.

What are the Facts of about Database Transaction?

Below are some facts of database transaction are:

1. Database Management System transactions must be consistent, atomic,durable and isolated.
2. It is executed at one unit only.
3. A successful transaction can modify the database from one CONSISTENT STATE to another.
4. A transaction is a program unit whose execution may or may not change the contents of a database.