All Concept Of Database

All Concept Of Database :- A database is a collection of logically related information in an organised way so that it can be easily accessed, managed and updated. Some other operations can also be performed on database such as adding, updating and deleting data. A database could be insimple as a single text file with a list of names or it could be complex as a large bunch of text files including sone data.

A Database is a collection of data that is stored in a computer system. Database allow their users to enter, access, and analyze their data quickly and easily. They’re such a useful tool that you see them all the time.

The generalized architecture of a database system ia called the ANSI/SPARC (American National Standards Institute/Standards Planning and requirement committee) model. Many commercial system and research database models fit within this framework.

Fundamentals of Database 

For defining database, two terms, which are used frequently with database, should be known.

1. Data: These are raw and unorganised facts that need to be procceed such as digital representation of text, numbers, graphical images or sound. e.g. a students test score is one piece of data.
2. Information: When data is processed, organised, structured or presented in a given context to make it useful or meaningful, it is called information. e.g. the classes average score is the information that can be concluded from the given data.

Types of Database

Database are three types, namely as follows:

• Network Database:- In this type of database, data is represented as collection of records and relationships among data represented as links.
• Hierarchical Database:- In this type of database, data is organised in the form of tree with nodes. Nodes are connected via links.
• Relational Database:- This database is also known as structured database in which data is stored in the form of tables. Where, columns define the type of data stored in the table and rows define the information about the data.

Components of a Database

A Database consists of several different components. Each components listed, is called an object. Within the file, you can divide your data into separate storage containers called tables view, add and update table data by using online forms, find and retrieve the data that you want by using queries and analyse or print data in a specific layout by using reports.

Database components are described below:-

1. Tables: These are the building blocks or relation of any relational database model where all the actual data ia defined and entered. Different types of operation are done on the tables such as storing, filtering, retrieving and editing of data. Tables consists of cells at the intersection of record (rows) and fields (columns), which are described below:

• Field:- It is an area (within the record) reserved for a specific piece of data.e.g. customer number, customer name, street address, city, state, phone number, current address etc. Field of a table is also known as columns.
• Record: It is the collection of data items of all the fields pertaining to one entity, i.e. a person, company, transition, etc. Record of a table is also known as row or a tuple and the number of records in a relation is called the cardinality of that relation.

2. Queries: These are basically questions based on the data available in a database. A query consists of specifications indicating which fields, records, and summaries a user wants to fetch from a database. Queries allow you to extract data based on the criteria that you define.

3. Forms: Although you can enter and modify data in datasheet view of tables but you neither control the users action very well nor yoh can do much to facilitate the data-entry process. To overcome this problems, forms are introduced like tables, forms can be used to view and edit your data. However, forms are typically used to view the data in an underlying table one record at a time. People generally prefer to enter data into a well-designed from, rather than a table.

4. Reports: When you want to print those records which are fetched from your database, design a report. Access even has a wizard to help produce mailing labels.

Database Management System (DBMS) 

A DBMS is a collection of interrelated data and a set of program to retrieve data from a database. It is an organised collection of data viewed as a whole, instead of a group of separate unrelated files.

The primary goal of DBMS is to provide an environment that is both convenient and efficient for user to store and retrieve database information. Example my SQL, Oracle, FoxPro, MS access. The purpose of database management system is to bridge the gap between information and data.

The basic process that are supported by DBMS are as follows:

1. Specification of data types structures and constraints to be considered in an application.
2. Storing the data.
3. Manipulation of the database.
4. Querying the database to retrieve desired information.
5. Updating the content of the database.

Architecture of DBMS 

The generalized architecture of a database system is called the ANSI/SPARC (American National standards institute/standards planning and requirement committee) model. Many commercial system and research database model fit within this framework. The architecture as per as ANSI/SPARC.

It can be divided into the following three level:-

• External level or View level
• Conceptual Level
• Internal Level or Physical Level

External Level

This is the highest level of data abstraction which describes the interaction between the user and the system. It permits the user to access data in a way that is customised according to their needs, so that the same data can be seen by different users in different ways, at the same time. It is also known as view level.

The External or View Level of the architecture of a Database system is the level closet to the users. This level is concerned with the way in which data are observed by individuals. Most of the users of database are not concerned instead they need only part of the database relevant to them.

A (DBMS) Database Management System may provide many different view for the same database interrelation among the three levels of abstraction and present the stored data at three different levels.

Conceptual Level

It is the overall view of the databased and include all the information that is going to be represented in the database.

It describe what type of data is stored in the database the relationship among the data without effective to the physical level it is also known as logical level.

This level also indicates the relationships existing among data items. At this level, a database is described logically rather than physically in term of data structure. Users of this level are not concerned with how these logical data structures will be implemented at the physical level. Rather, there only concerned about what information would be kept in a database.

Internal Level (Physical Level)

The lowest level of abstraction is the internal level. It is the one closest to physical storage device. This level is also termed as physical level, because it describe how data are actually stored on the storage medium, such as hard disk, magnetic tap etc.

Advantages of DBMS

• Reduction in Data Redundancy:- The duplication of data refers to data redundancy DBMS cannot make separate copies of the same data. All the data is kept at a place and different application refer to data from centrally control system.
• Better Interaction with Users:- In DBMS, the availability of up to date information improve the data to be access or respond as per user request.
• Improvement in Data Security:- DBMS can allow the means of access to the database through the authorised channels to ensure security DBMS provide security tool that is username and password.
• Maintenance Of the Data Integrity:- Data integrity in show that the data of database is accurate. In DBMS, data is centralised and used by many users at a time it is essential to enforce integrity controls.
• Ease of Application Development:- The application programmer needs to develop the application programs according to the users need. The other issues like concurrent access, security, Data integrity, etc, are handed by database itself. This makes the application development an easier task.
• Backup and Recovery:- The DBMS provides breakup and recovery subsystem that is responsible to recover data from hardware and software failure.

Disadvantages Of DBMS

• Cost of Hardware and Software:- A processor with high speed of data processing and memory of large size is required to run the DBMS software it means that you have to upgrade the hardware used for file base system similarly database software is also very costly.
• Complexity:- The provision of the functionality that is expected from a good DBMS makes the DBMS and extremely complex peace of software failure to understand the system can lead to bad designed disease decision which can have serious consequence for an organisation.
• Cost of the Staff Training:- Mostly DBMS are often complex system so the training for user to use the database is required the organisation has to pay a lot of amount for the training of staff to run the DBMS.
• Appointing Technical Staff:- The trained technical person such as database administrator application programmers extra are required to handle the database you have to pay a lot of amount to this person there for a system cost increases.
• Database Failure:- In most of the organisation all data is integrated into a single data based if database is corrupted due to power failure or it is corrupted on the storage media then our valuable data may be lost or whole system is stop.

Data Independance 

A database is viewed through any of the three levels of abstraction. Any change at any level may affect other level’s scheme (structure of database). As the databases keep growing, there may be changes made at some level. However, this should never lead to redesigning and re-implementation of a database. This concept of data independance proves beneficial in such a context.

There are two levels of data independence. These are as follows:

• Physical
• Logical

Physical Data Independance 

Physical Data Independance refers to the ability to modify the schema followed at the physical level without affecting the schema followed at a conceptual level. That is, the application programs remain the same even though the schema at physical level gets modified.

Logical Data Independance 

Logical Data Independance refers to the ability to modify the conceptual schema without causing any changes in the schema followed at view level. The logical data Independance ensures that the application programs remain the same. Modification at the conceptual level are necessary whenever logical structures of the database get altered because of some unavoidable reasons. Such a case may be the introduction of maternity leave for female employee table.

The abstract data types in modern programming languages implement concept of data independance to a larger extent. Both types hide implementation details from the users. This allows users to concentrate on the general structure rather than low level implementation details.

Database Models 

A Database model is a collection of toola for describing data, data relationships, data semantic and consistency constraints. Data base models can be broadly classified into the following categories:-

• Conceptual database Models
• Physical Database Models
• Logical Database Models

Conceptual Database Models

The conceptual database models are used in describing data at the conceptual level and also at the view level. They provide the flexible structuring capabilities. A number of conceptual models have been proposed, but Entity – Relationships (ER) model is widely used. They are also known as object based database models.

Physical Database Models 

Physical database models are used to describe data at the lowest level. With the physical models it is possible to implement the database at the system level. Two of the widely known models are unifying model and frame memory model.

Logical Database Models 

Logical Database Models are also used in describing data at the conceptual and view levels. However, in contrast to conceptual database models, these models are used to specify both the over all logical structure of the database and a higher level description of the implementation. They are also known as record based database models.

There are three types of record based data models. These are the following:-

1. Hierarchical Data Model
2. Network Data Models
3. Relational Data Models

Application of DBMS

Some application of DBMS are as follows:-

1. Banking:- For Customer information, accounts, loans and other banking transaction.
2. Universities:- For students information, course registration, grades etc.
3. Reservation:- For reservation and schedule information.
4. Credit Card Transaction:- For purpose of credit cards and generation of monthly statements.
5. Telecommunication:- For keeping records of call made, generating monthly bill, etc.
6. Finance:- For Storing information about holdings, sales and purchase of financial statements.
7. Sales:- For customer, product and purchase information.

Relational Database 

In a Relational Database, data is stored in different tables with relationships to each other. These tables communicate and share information, which facilitates data search ability, organisation and reporting. In the case of relational database, a Relational Database Management System (RDBMS) performs these tasks. An important feature of this database system is that a single database can be spread across several tables.

Example:- Base, Oracle, DB2, SAP SyBase, Informix etc.

Terms Related to Database

Various terms related to relational database are ad follows:-

1. Relational:- It is a table with columns and rows which represent in the data items and relationships among them. Relation have three important properties a name, cardinality and a degree.

• Name:- The first property of a relation is its name, which is represented by the tide or the entity identifier.
• Cardinality:- The second property of a relations is its cardinality, which refers to the number of tuples (rows) in a relation.
• Degree:- The third property of a relation is its degree, which refers to the number of attributes (columns) in each tuple.

2. Domain:- It is a collection of all possible values from which the values for a given columns or an attributes is drawn. A domain is said to be atomic if elements are considered to be indivisible units.

3. Attributes:- The heading columns of a table are known as attributes. Each attribute of a table has a distict name.

4. Tuples:- The rows in a relation are also known as tuples. Each row or tuple has a set of permitted values for each attributes.

Database Languages 

There are various types of databases language

• Data Definition Language (DDL) :- DDL is used to define structure of your tables and other objects in database. In DBMS, it is used to specify a database schema as a set of definitions.
• Data Manipulation Language:- DML provides various commands used to access and manipulate data in existing database. This maipulation involves inserting data into data base tables retrieving existing data, deleting data from existing tables and modifying existing data.
• Data Control Language:- DCL commands are used to assign security levels in database which involves multiple user setups. They are used to grant defined role and access privilages to the user.