What is dbms ?
Data is a very important resource in the operation and management of an organization. So, it is very essential to organize the data in a meaningful manner, because an unorganized data has no meaning.
With the increased demand of the data in the various organizations such as banks, universities, railways, airlines, companies etc., it becomes a necessity to store data in an organized manner so that it can be used again and again. So, we need a database to store the data in an organized form.
Database can be defined as “A well organized collection of data that are related in a meaningful way, which can be accessed by different users but stored only once”.
To understand the concept of database, let us consider an example of telephone directory in which names of people are arranged in an alphabetical order.
So, it becomes easier to search any phone number corresponding to a particular name. If this ordering is not done in an organized manner then it is very difficult to search a phone number of a particular person, so this shows why database are needed.
DBMS Consists of two parts
2. Management system
To find out what database is, we have to start from data, which is the basic building block of any database management system.
What is Data ?
It is a raw set of facts and figures associated with an individual, an entity, or an event. It is basically a collection of unorganized facts or concepts that does not convey any meaning. Data can be represented in various forms i.e. in figures, characters, symbols, pictures, audio, video etc.
What is Record ?
A record can be defined as a collection of related data items, e.g. in the above example the three data items (1, ANSH, 19) had no meaning.
But if we organize them in the following way, then they collectively represent meaningful information or a record.
What is Table ?
Table : Collection of related records marks a table. the columns of the table are called fields, attributes or domains. The rows are called Tuples or records. Table is also known as a Relation.
What is Database?
Database: Collection of related tables makes a Database. Consider the following collection of tables:
Now, we have a collection of 4 tables. They can be called a “related collection” because we can clearly find out that there are some common attributes existing in a selected pair of tables.
Because of these common attributes we may combine the data of two or more tables together to find out the complete details of a student.
Questions like “Which hostel does the youngest student live in?” can be answered now, although Age and Hostel attributes are in different tables.
In a database, data is organized strictly in row and column format. The rows are called Tuple or Record. The data items within one row may belong to different data types. On the other hand, the columns are often called Domain or Attribute. All the data items within a single attribute are of the same data type.
What is Management System ?
A management system is a set of rules and procedures which help us to create organize and manipulate the database.
It also helps us to add, modify delete data items in the database. The management system can be either manual or computerized.
The management system is important because without the existence of some kind of rules and regulations it is not possible to maintain the database.
We have to select the particular attributes which should be included in a particular table; the common attributes to create relationship between two tables; if a new record has to be inserted or deleted then which tables should have to be handled etc.
These issues must be resolved by having some kind of rules to follow in order to maintain the integrity of the database.
“DBMS (Database Management System) is a software system used to manage database and its various operations like insertion, deletion, updation and retrieval.
It enables users to store, modify and extract information from a database as per the requirements. It acts as an intermediator between the user and the database.”
To maintain huge databases, we need certain operations which help in maintaining the data in the database efficiently.
The most commonly used operations performed on the databases are:
To add new data into the database. (For example: To add new phone number into the telephone directory.)
To view or retrieve the stored data. (For example: To view a telephone number of a particular person from the telephone directory.)
To modify or edit the existing data. (For example: Suppose the phone number of a particular person is changed, so we have to modify the telephone directory by replacing his old phone number with a new phone number.)
To remove or delete the existing data from the database. (For example: Suppose an employee has left the organization, so his record should be deleted from the employee database of the organization.)
To arrange the data in a desired order (ascending/ descending). (For example: In employee database of an organization, records should be arranged in an alphabetical order for easy and fast retrieval.)
The collection of data, usually referred to as the database, contains information relevant to an enterprise. Today, database systems are widely used to manage large bodies of information.
Some of the important database applications are:
(a) Banking: For customer information, accounts, and loans, and banking transactions.
(b) Universities: For student information, course registrations, results and
(c) Airlines: For reservations and schedule information. Airlines were among the first to use databases in a geographically distributed manner- terminals situated around the world accessed the central database system through phone lines and other data networks.
(d) Credit card transactions: For purchases on credit cards and generation of
monthly statements. (e) Sales: For customer, product, and purchase information.
(1) Telecommunication: For keeping records of calls made, generating monthly bills, maintaining balances on prepaid calling cards, and storing information about the communication networks.
(g) Manufacturing: For tracking production of items in factories, inventories of items in warehouses/stores, and orders for items.
(h) Human resources: For information about employees, salaries and payroll taxes etc.
APPROACHES TO DATA MANAGEMENT
With the advancements in computer technology, there was a need to computerize the manual way of storing the data in database.
Two approaches used for data management through computers are:
(i) File-Based Approach
(ü) Database Approach
File-Based approach was an early attempt to computerize the manual filing system. It is basically a collection of application programs that performed services for the end users. Each program within a file based system defines and manages its own data. In this system, a large number of files are needed to perform various
This approach to data management, in which separate data files are created and stored for each application program, is called the Traditional File Approach.
Characteristics of File-Based Approach
Some important characteristics of File-Based approach are:
- It is a group of files storing data of an organization. . Each file is independent from one another.Each file is called a flat file.
- Each file contained and processed information for one specific task, such as accounting or inventory.
- Files are designed by using programs written in programming languages.such as C, C++.
- Each file must have its own file management system.
Drawbacks of File-Based Approach
As systems became more complex, file system approach offered little flexibility, presented many limitations, and was difficult to maintain.
Following are the drawbacks of File-Based approach:
⚫ Data Redundancy: Data redundancy means duplication of data values, i.e. same information is duplicated in several files. This makes data redundancy. Duplication is wasteful. It costs time and money to enter the data more than once and also take up additional storage space.
⚫ Data Inconsistency: Data inconsistency means different copies of the same data are not matching. That means different versions of same basic data are existing in different files. This occurs as the result of update operations that are not updating the same data stored at different places. E.g. Address information of a customer is recorded differently in different files.
⚫ Data Isolation: Data are scattered in various files, and the files may be in different format, writing new application program to retrieve data is difficult.
⚫ Integrity Problems: The data values may need to satisfy some integrity constraints. For example: The balance field value must be grater than 5000. We have to handle this through program code in file processing systems. But in database we can declare the integrity constraints along with definition itself.
⚫ Atomicity Problem: It is difficult to ensure atomicity in file processing system. For example: Transferring $100 from Account A to Account B. If a failure occurs during execution there could be situation like $100 is deducted from Account A and not credited in Account B.
⚫ Concurrent Access variation: If multiple users are updating the same data simultaneously, it will result in inconsistent data state. In file processing system it is very difficult to handle this using program code. This results in concurrent access variation.
⚫ Security Problems: Enforcing security constraints in file processing system is very difficult as the application programs are added to the system in an unplanned or informal manner.
In order to remove all the above limitations of the File-based approach, a new approach was required that must be more effective. So, the concept of database was introduced. This approach is known as database approach.
A database is a computer based record keeping system whose over all purpose is to record and maintains information. The database is a single, large repository of data, which can be used simultaneously by many departments and users. With the database approach, instead of disconnected files with redundant data, all data items are integrated with minimum amount of duplication and maintained only at one location. In this approach, related data is shared by multiple application programs.
Characteristics of Database Approach
A database approach possesses the following characteristics:
- It is central repository of shared data. It allows several users to access the database concurrently.
- A fundamental feature of the database approach is that the database system does not only contain the data but also the complete definition and description of these data.
- These descriptions are basically details about the extent, the structure, the type and the format of all data and, additionally, the relationship between the data. This kind of stored data is called metadata (“data about data”).
- A primary feature of the database approach is a standardized, uniform approach to database access. This means that the same overall procedures are used by all application programs to retrieve data and information.
- Data should be correct with respect to the real world entity that they represent.
- . Data should be protected from unauthorized access.
- Its organization is such that duplication of data is minimized. Data in a database exist permanently until it is not explicitly deleted.
Drawbacks of Database Approach
Following are the drawbacks of Database approach:
- Database management systems can be difficult to set up and operate. Many decisions must be made correctly for the database management system to work effectively. In addition, users have to learn new procedures to take full advantage of a database management system.
- With the traditional approach to file management, a failure of a file only affects a single program. But with a database management system, a failure can shut down the entire database.
- Database management systems can be more expensive to purchase and operate. The expense includes the cost of the database and specialized personnel, such as database administrator, who is needed to design and operate the database.
- Recovery is more complex.
- Initial training required for all programmers and users.
ADVANTAGES OF DBMS
DBMS (Database management system) has following advantages:
The data in a DBMS is more concise because, as a general rule, the information in it appears just once. This reduces data redundancy, because redundancy is the problem of storing the same data item in more than one place. Redundancy creates several problems like requiring extra storage space, entering same data more than once during data insertion, and deleting data from more than one place during deletion. Minimizing redundancy can therefore significantly reduce the cost of storing information on hard drives and other storage devices and wastage of time in entering data again and again.
Elimination of Inconsistency
In the file processing system information is duplicated throughout the system. So changes made in one file may be necessary be carried over to another file. This may lead to inconsistent data. So we need to remove this duplication of data in multiple file to eliminate inconsistency. DBMS centralize the entire database so that changes once made are reflected to all the tables where a particulars field is stored.
Sharing of Data
In a paper-based record keeping, data cannot be shared among many users. But in computerized DBMS, many users can share the same database if they are connected through a network.
We can restrict certain people from accessing the database or allow them to see certain portion of the database while blocking sensitive information. This is not possible very easily in a paper-based record keeping.
Flexibility of the System is improved
Since changes are often necessary to the contents of the data stored in any system, these changes are made more easily in a centralized database than in a conventional system. Applications programs need not to be changed on changing the data in the database.
Standards can be enforced
Since all access to the database must be through DBMS, so standards are easier to enforce. Standards may relate to the naming of data, format of data, structure of the data etc. Standardizing stored data formats is usually desirable for the purpose of data interchange or migration between systems.
Accurate, consistent, and up-to-date data is a sign of data integrity. DBMS supports data integrity. Data integrity means that the data contained in the database is both accurate and consistent. Therefore, data values being entered for storage could be checked to ensure that they fall within a specified range and are of the correct format. Moreover updates and changes to the data only have to be made in one place. The chances of making a mistake are higher if you are required to change the same data in several different places than if you only have to make the change in one place.
Provides Backup and Recovery: Centralizing a database provides the schemes such as recovery and backups from the failures including disk crash, power failures, software errors which may help the database to recover from the inconsistent state to the state that existed prior to the occurrence of the failure, though methods are very complex.
DISADVANTAGES OF DBMS
However, there could be a few disadvantages of using DBMS. They can be as following:
High Cost: A significant disadvantage of the DBMS system is cost. As DBMS needs computers, we have to invest a good amount in acquiring the hardware, software, installation facilities and training of users.
Complexity of Backup and Recovery: While centralization reduces duplication, the lack of duplication requires that the database be adequately backed up so that in the case of failure the data can be recovered. Backup and recovery operations are fairly complex in a DBMS environment. We have to keep regular backups because a failure can occur any time. Taking backup is a lengthy process and the computer system cannot perform any other job at this time.
Security Threats: Even with safeguards in place, it may be possible for some unauthorized users to access the database. So, security system must be very robust. If someone can bypass the security system then the database would become open to any kind of mishandling