RDBMS_Unit_I

Unit-I		Unit-II	Unit-III	Unit-IV	Unit-V
Part-I	Part-II	Part-I	Part-I	Part-I	Total
Part-III	Part-IV	Part-II	Part-II	Part-II
Part-V		Part-III

                                                    Unit-1 

BASIC CONCEPTS 

 Introduction 

A database to be a collection of related data . A database management system (DBMS) is the software that manages and controls access to the database. A database application is simply a program that interacts with the database at some point in its execution.

  Characteristics of DBMS •

It uses a digital repository established on a server to store and manage the information. • It can provide a clear and logical view of the process that manipulates data.

• DBMS contains automatic backup and recovery procedures. • It contains ACID properties which maintain data in a healthy state in case of failure. 

• It can reduce the complex relationship between data. 

• It is used to support manipulation and processing of data.

 • It is used to provide security of data.

 • It can view the database from different viewpoints according to the requirements of the user.

  Database will be used in following scenarios 

1. Purchases from the supermarket 

2. Purchases using your credit card 

3. Booking a vacation with a travel agent 4. Using the local library

 5. Taking out insurance 

6. Renting a DVD 

7. Using the Internet 

8. Studying at College 

 Functions of a dbms 1.What are the functions of Dbms? Explain?

 Ans: 

 (1) Data storage, retrieval, and update 

A DBMS provides users with the ability to store, retrieve, and update data in the database and it provides a catalog in which descriptions of data items are stored and which is accessible to users. (2) A user-accessible catalog 

A DBMS must provide a catalog in which descriptions of data items are stored and is accessible to users. (3) Transaction support 

 A transaction is a series of actions, carried out by a single user or application program, which accesses or changes the contents of the database. (4) Concurrency control services 

The DBMS must ensure that when multiple users are accessing the database, interference cannot occur. (5) Recovery services 

A DBMS must furnish a mechanism for recovering the database in the event that the database is damage or failure. 

 (6) Authorization services

 A DBMS must furnish a mechanism to ensure that only authorized users can access the database. (7) Support for data communication 

A DBMS must be capable of being integrated with a variety of Data Communications Managers (DCMs) to handle communication messages. 

 (8) Integrity services 

Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate. (9) Services to promote data independence 

A DBMS must include facilities to support the independence of programs from the actual structure of the database. (10) Utility services 

Examples of utilities of the latter kind are:

 • Monitoring facilities, to monitor database usage and operation. 

•Index reorganization facilities, to reorganize indexes and their overflows.

 •Garbage collection and reallocation, to remove deleted records. 

THE FILE BASED SYSTEM 

2. What are the Limitations of File Based Approach?

 Limitations of the File-Based Approach Ans: 

1. Separation and isolation of data 

When data is in separate files, it is more difficult to access data . This difficulty is arises if we require data from more than two files. 

 2. Duplication of data 

• Duplication is wasteful. It costs time and money to enter the data more than once. 

• It takes up additional storage space, again with associated costs. 3. Data dependence 

The physical structure and storage of the data files and records are defined in the application code. This means that changes to an existing structure are difficult to make. Clearly, this process could be very time-consuming and subject to error. 4. Incompatible file formats 

For example, the structure of a file generated by a COBOL program may be different from the structure of a file generated by a C program. The direct incompatibility of such files makes them difficult to process jointly. 5. Fixed queries/proliferation of application programs 

In some organizations, the type of query or report that could be produced was fixed. There was no facility for asking unplanned queries either about the data itself or about which types of data were available. In other organizations, there was a proliferation of files and application programs. 

THE DATABASE APPROACH

 3. Explain Database Approach? 

Ans:

In order to overcome the limitations of a file system, a new approach was required. Hence a database approach emerged. A database is a persistent collection of logically related data.

  The database is a single, possibly large repository of data. 

  That can be used by many departments and users simultaneously.  All data items are integrated with a minimum amount of duplication. 

  The database not owned by one department but is a shared corporate resource.

  The database holds not only the organization’s operational data, but also a description of this data. 

  The description of the data is known as the system catalog (or data dictionary or metadata—the “data about data”). DBMS controls access to this data and thus needs to provide features for database creation, data manipulation such as data value modification, data retrieval, data integrity and security etc.

  

 4. Explain advantages of Dbms over file based System? 

Ans: Advantages of dbms over file based system 

  Control of data redundancy 

 The database approach attempts to eliminate the redundancy by integrating the files so that multiple copies of the same data are not stored.  Data consistency 

By controlling redundancy, we reduce the risk of inconsistencies occurring. If a data item is stored only once in the database, any update to its value has to be performed only once and the new value is available immediately to all users. improves data consistency. 

  More information from the same amount of data 

 With the integration of the operational data, it may be possible for the organization to derive additional information from the same data.  Sharing of data 

 The database belongs to the entire organization and can be shared by all authorized users. In this way, more users share more of the data. 

  Improved data integrity 

 Database integrity refers to the validity and consistency of stored data. Integrity is usually expressed in terms of constraints, which are consistency rules that the database is not permitted to violate.  Improved security 

 Database security is the protection of the database from unauthorized users. This security may take the form of user names and passwords to identify people authorized to use the database.

  Enforcement of standards 

 Database integration allows the DBA to define and the DBMS to enforce the necessary standards. These may include departmental, organizational, national, or international standards for such things as data formats to facilitate exchange of data between systems, naming conventions, documentation standards, update procedures, and access rules.  Economy of scale 

 Combining all the organization’s operational data into one database and creating a set of applications that work on this one source of data can result in cost savings leading to an economy of scale.

  Balance of conflicting requirements 

 The database is under the control of the DBA, the DBA can make decisions about the design and operational use of the database.  Improved data accessibility and responsiveness 

 The database integrity feature provides the data be directly accessible to the end-users. This provides more functionality and better services to the end-users.

  Increased productivity 

Many DBMSs provide a fourth-generation environment with tools that simplify the development of database applications. This results in increased programmer productivity and reduced development time.  Improved maintenance through data independence 

 A DBMS separates the data descriptions from the applications, thereby making applications immune to changes in the data descriptions. This is known as data independence.

 Increased concurrency 

 Many DBMSs manage concurrent database access and ensure that such problems cannot occur. DBMSs employs various concurrency control techniques.  Improved backup and recovery services 

 Modern DBMSs provide facilities to minimize the amount of processing that is lost following a failure. They also provide automatic backup facilities.