DBMS

Explain DBMS?

        A DBMS is best described as a collection of programs that manage the database structure and that control shared access to the data in the database. Current DBMSes also store the relationships between the database components; they also take care of defining the required access paths to those components

      A database management system (DBMS) is the combination of data, hardware, software and users to help an enterprise manage its operational data.

      The main function of a DBMS is to provide efficient and reliable methods of data retrieval to many users. Efficient data retrieval is an essential function of database systems. DBMS must be able to deal with several users who try to simultaneously access several items and most frequently, the same data item A DBMS is a set of programs that is used to store and manipulation data that include the following:

      • Adding new data, for example adding details of new student.

      • Deleting unwanted data, for example deleting the details of students who have  

       completed course.

      • Changing existing data, for example modifying the fee paid by the student.

Components of DBMS

     A database system has four components. These four

components are important for understanding and designing the database system. These

are:

      1. Data

      2. Hardware

      3. Software

      4. Users

1. Data

     A Data item is the smallest unit of named data: It may consist of bits or bytes. A Data item is often referred to as field or data element. A Data aggregate is the collection of data items within the record, which is given a name and referred as a whole. Data can be collected orally or written. A database can be integrated and shared. Data stored in a system is partition into one or two databases. So if by chance data lost or damaged at one place, then it can be accessed from the second place by using the sharing facility of data base system. So a shared data also cane be reused according to the user’s requirement. Also data must be in the integrated form. Integration means data should be in unique form i.e. data collected by using a well-defined manner with no redundancy, for example Roll number in a class is non-redundant form and so these have unique resistance, but names in class may be in the redundant form and can create lot of problems later on in using and accessing the data.

2. Hardware

      Hardware is also a major and primary part of the database. Without hardware nothing can be done. The definition of Hardware is “which we can touch and see”, i.e. it has physical existences. All physical quantity or items are in this category. For example, all the hardware input/output and storage devices like keyboard, mouse, scanner, monitor, storage devices (hard disk, floppy disk, magnetic disk, and magnetic drum) etc. are commonly used with a computer system.

3. Software

      Software is another major part of the database system. It is the other side of hardware. Hardware and software are two sides of a coin. They go side by side. Software is a system. Software are further subdivided into two categories, First type is system software (like all the operating systems, all the languages and system packages etc.) and second one is an application software (payroll, electricity billing, hospital management and hostel administration etc.). We can define software as which we cannot touch and see. Software only can execute. By using software, data can be manipulated, organized and stored. -

4. Users

      Without user all of the above said components (data, hardware & software) are meaning less. User can collect the data, operate and handle the hardware. Also operator feeds the data and arranges the data in order by executing the software. Other components

      1. People - Database administrator; system developer; end user.

      2. CASE tools: Computer-aided Software Engineering (CASE) tools.

      3. User interface - Microsoft Access; PowerBuilder.

      4. Application Programs - PowerBuilder script language; Visual Basic; C++; COBOL.

      5. Repository - Store definitions of data called METADATA, screen and report formats, menu definitions, etc.

     6. Database - Store actual occurrences data.

      7. DBMS - Provide tools to manage all of this - create data, maintain data, control security access to data and to the repository, etc.

Various functions of DBMS

• Data definition: The DBMS must be able to accept data definitions (external schemas, the conceptual schema, the internal schema, and all associated mappings) in source form and convert them to the appropriate object form.

      • Data manipu1ation: The DBMS must be able to handle requests from the users to retrieve, update, or delete existing data the database, or to add new data to the database. In other words, the DBMS must include a data manipulation language (DML) processor component.

      • Data security and integrity: The DBMS must monitor user requests and reject

any attempt to violate the security and integrity rules defined by the DBA.

      • Data recovery and concurrency: The DBMS - or else some other related software component, usually called the transaction manager - must enforce certain recovery and concurrency controls.

      • Data Dictionary: The DBMS must provide a data dictionary function. The data dictionary can be regarded as a database in its own right. The dictionary contains “data about the data” (sometimes called metadata) - that is, definitions of other objects in the system - rather than just”raw data.” In particular, all the various schemas and mapping (external, conceptual, etc.) will physically be stored, in both source and object form, in the dictionary. A comprehensive dictionary will also include cross- reference information, showing, for instance, which programs use which pieces of the database, which users require which reports, which terminals are connected to the system, and so on. The dictionary might even - in fact, probably should — be integrated into the database it defines, and thus include its own definition. It should certainly be possible to query the dictionary just like any other database, so that, for example, it is possible to tell which programs and or users are likely to be affected by some proposed change to the system.

ADVANTAGES OF DBMS

      One of the major advantages of using a database system is that the organization

can be handled easily and have centralized management and control over the data by the DBA. Some more and main advantages of database management system are given below:

      The main advantages of DBMS are:

1. Controlling Redundancy

      In a DBMS there is no redundancy (duplicate data). If any type of duplicate data arises, then DBA can control and arrange data in non-redundant way. It stores the data on the basis of a primary key, which is always unique key and have non-redundant information. For example, Roll no is the primary key to store the student data.

In traditional file processing, every user group maintains its own files. Each group independently keeps files on their db e.g., students. Therefore, much of the data is stored twice or more. Redundancy leads to several problems:

     

      • Duplication of effort

      • Storage space wasted when the same data is stored repeatedly

      Files that represent the same data may become inconsistent (since the updates are applied independently by each users group).We can use controlled redundancy.

2. Restricting Unauthorized Access

      A DBMS should provide a security and authorization subsystem.

      • Some db users will not be authorized to access all information in the db (e.g., financial data).

      • Some users are allowed only to retrieve data.

      • Some users are allowed both to retrieve and to update database.

3. Providing Persistent Storage for Program Objects and Data Structures

      Data structure provided by DBMS must be compatible with the programming language’s data structures. E.g., object oriented DBMS are compatible with programming languages such as C++, SMALL TALK, and the DBMS software automatically performs conversions between programming data structure and file formats.

4. Permitting Inferencing and Actions Using Deduction Rules

      Deductive database systems provide capabilities for defining deduction rules for inferencing new information from the stored database facts.

5. Inconsistency can be reduced

      In a database system to some extent data is stored in, inconsistent way. Inconsistency is another form of delicacy. Suppose that an em1oyee “Japneet” work in department “Computer” is represented by two distinct entries in a database. So way inconsistent data is stored and DBA can remove this inconsistent data by using DBMS.

6. Data can be shared

      In a database system data can be easily shared by different users. For example, student data can be share by teacher department, administrative block, accounts branch arid laboratory etc.

7. Standard can be enforced or maintained

      By using database system, standard can be maintained in an organization. DBA is overall controller of database system. Database is manually computed, but when DBA uses a DBMS and enter the data in computer, then standard can be enforced or maintained by using the computerized system.

8. Security can be maintained

      Passwords can be applied in a database system or file can be secured by DBA. Also in a database system, there are different coding techniques to code the data i.e. safe the data from unauthorized access. Also it provides login facility to use for securing and saving the data either by accidental threat or by intentional threat. Same recovery procedure can be also maintained to access the data by using the DBMS facility.

9. Integrity can be maintained

      In a database system, data can be written or stored in integrated way. Integration means unification and sequencing of data. In other words it can be defined as “the data contained in the data base is both accurate and consistent”. ‘Data can be accessed if it is

compiled in a unique form. We can take primary key ad some secondary key for integration of data. Centralized control can also ensure that adequate checks are

incorporated in the DBMS to provide data integrity.

10. Confliction can be removed

      In a database system, data can be written or arranged in a well-defined manner by DBA. So there is no confliction between the databases. DBA select the best file structure and accessing strategy to get better performance for the representation and use of the

data.

11. Providing Multiple User Interfaces

      For example query languages, programming languages interfaces, forms, menu- driven interfaces, etc.

12. Representing Complex Relationships Among Data

      It is used to represent Complex Relationships Among Data

13. Providing Backup and Recovery

      The DBMS also provides back up and recovery features.

DISADVANTAGES OF DBMS

      Database management system has many advantages, but due to some major problem  arise in using the DBMS, it has some disadvantages 

1.Cost

      A significant disadvantage of DBMS is cost. In addition to the cost of purchasing or developing the software, the organization *111 also purchase or upgrade the hardware

and so it becomes a costly system. Also additional cost occurs due to migration of data

from one environment of DBMS to another environment.

2. Problems associated with centralization

      Centralization also means that data is accessible from a single source. As we know the centralized data can be accessed by each user, so there is no security of data from unauthorized access and data can be damaged or lost.

3. Complexity of backup and recovery

      Backup and recovery are fairly complex in DBMS environment. As in a DBMS, if you take a backup of the data then it may affect the multi-user database system which is in operation. Damage database can be recovered from the backup floppy, but iterate duplicacy in loading to the concurrent multi-user database system.

4. Confidentiality, Privacy and Security

      When information is centralized and is made available to users from remote locations, the possibilities of abuse are often more than in a conventional system. To reduce the chances of unauthorized users accessing sensitive information, it is necessary to take technical, administrative and, possibly, legal measures. Most, databases store valuable information that must be protected against deliberate trespass and destruction.

5. Data Quality

      Since the database is accessible to users remotely, adequate controls are needed to control users updating data and to control data quality. With increased number of users accessing data directly, there are enormous opportunities for users to damage the data. Unless there are suitable controls, the data quality may be compromised.

6. Data Integrity

      Since a large number of users could be using .a database concurrently, technical safeguards are necessary to ensure that the data remain correct during operation. The main threat to data integrity comes from several different users attempting to update the same data at the same time. The database therefore needs to be protected against inadvertent changes by the users.

7. Enterprise Vulnerability

      Centralizing all data of an enterprise in one database may mean that the database becomes an indispensable resource. The survival of the enterprise may depend on reliable information being available from its database. The enterprise therefore becomes vulnerable to the destruction of the database or to unauthorized modification of the database.

8. The Cost of using a DBMS

      Conventional data processing systems are typically designed to run a number of well-defined, preplanned processes. Such systems are often “tuned” to run efficiently for the processes that they were designed for. Although the conventional systems are usually fairly inflexible in that new applications may be difficult to implement and/or expensive to run, they are usually very efficient for the applications they are designed for.

      The database approach on the other hand provides a flexible alternative where new applications can be developed relatively inexpensively. The flexible approach is not without its costs and one of these costs is the additional cost of running applications that the conventional system was designed for. Using standardized software is almost always less machine efficient than specialized software.