III BCOM(CA) - DBMS - UNIT-1 Notes

Unit-I: Data and Information,File, Database, Database Management System, Objectives of DBMS, Evolution of Database Management Systems, Classification of Database Management System.

Q) Define a) Data  b) Information c) File

Answer:

a) Data:- Data is the known facts or figures that have implicit meaning. It can also be defined as it is the representation of facts ,concepts or instruction in a formal manner, which is suitable for understanding and processing.  Data can be represented in alphabets(A-Z, a-z),in digits(0-9) and using special characters(+,-.#,$, etc)

e.g: 25, “ajit” etc.

b) Information:- Information is the processed data on which decisions and actions are based. Information can be defined as the organized and classified data to provide meaningful values.

Eg: “The age of Ravi is 25”

C) File:- File is a collection of related data stored in secondary memory

Q) Define DBMS. Explain some functions/Objectives of DBMS.

Answer:

Database Management System (DBMS): A database management system consists of collection of related data and refers to a set of programs for defining, creation, maintenance and manipulation of a database.

Functions of DBMS

1. Defining database schema: it must give facility for defining the database structure also specifies access rights to authorized users.

2. Manipulation of the database: The dbms must have functions like insertion of record into database updation of data, deletion of data, retrieval of data

3. Sharing of database: The DBMS must share data items for multiple users by maintaining consistency of data.

4. Protection of database: It must protect the database against unauthorized users.

5. Database recovery: If for any reason the system fails DBMS must facilitate data base recovery.

Q) Explain the Evolution of Database Management Systems

File-based system was the predecessor to the database management system.

The chronological order of the development of DBMS is as follows:

–    Flat files – 1960s–1980s

–    Hierarchical – 1970s–1990s

–    Network – 1970s–1990s

–    Relational – 1980s–present

–    Object-oriented – 1990s–present

–    Object-relational – 1990s–present

–    Data warehousing – 1980s–present

–    Web-enabled – 1990s–present

Early 1960s. Charles Bachman at GE created the first general purpose DBMS Integrated Data Store. It created the basis for the network model which was standardized by CODASYL (Conference on Data System Language).

Late 1960s. IBM developed the Information Management System (IMS). IMS used an alternate model, called the Hierarchical Data Model.

1970. Edgar Codd, from IBM created the Relational Data Model. In 1981 Codd received the Turing Award for his contributions to database theory. Codd Passed away in April 2003.

1976. Peter Chen presented Entity-Relationship model, which is widely used in database design.

1980. SQL developed by IBM, became the standard query language for databases.

SQL was standardized by ISO.

1980s and 1990s. IBM, Oracle, Informix and others developed powerful DBMS

Q) Briefly explain the Classification of Database Management System.

Answer:

The database management system can be broadly classified into

(1) Passive Database Management System and

(2) Active Database Management System:

1. Passive Database Management System:  Passive Database Management Systems are program-driven. In passive database management system the users query the current state of database and retrieve the information currently available in the database. Traditional DBMS are passive in the sense that they are explicitly and synchronously invoked by user or application program initiated operations. Applications send requests for operations to be performed by the DBMS and wait for the DBMS to confirm and return any possible answers. The operations can be definitions and updates of the schema, as well as queries and updates of the data.
2. Active Database Management System. : Active Database Management Systems are data-driven or event-driven systems. In active database management system, the users specify to the DBMS the information they need.

If the information of interest is currently available, the DBMS actively monitors the arrival of the desired information and provides it to the relevant users. The scope of a query in a passive DBMS is limited to the past and present data, whereas the scope of a query in an active DBMS additionally includes future data. An active DBMS reverses the control flow between applications and the DBMS instead of only applications calling the DBMS, the DBMS may also call applications in an active DBMS.

Active databases contain a set of active rules that consider events that represent database state changes, look for TRUE or FALSE conditions as the result of a database predicate or query, and take an action via a data manipulation program embedded in the system. Alert is extension architecture at the IBM Almaden Research, for experimentation with active databases.