DBMS Midsem 2009

PART B

2.

    a)     Any input for processing for a required output known as data. Processed data is known as information. Data also can be information.

b)     A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose. 

               A DBMS is a system software package that helps the use of integrated collection of data records and files known as databases. It allows different user application programs to easily access the same database. Collection of information stored in a particular storage in organized way known as database.

4.The popularity of the network data model coincided with the popularity of the hierarchical data model. Some data were more naturally modeled with more than one parent per child. So, the network model permitted the modeling of many-to-many relationships in data.

5.In database technology, domain refers to the description of an attribute's allowed values. The physicaldescription is a set of values the attribute can have, and the semantic, or logical, description is the meaning of the attribute.

7. Unary Relationships

Unary relationships have only one participant-the relation is associated with itself. The classic example of a unary relationship is Employee to Manager. One's manager is, in most cases, also an employee with a manager of his or her own. 

8. Advantages

• Reduced data redundancy
• Reduced updating errors and increased consistency
• Greater data integrity and independence from applications programs
• Improved data access to users through use of host and query languages
• Improved data security
• Reduced data entry, storage, and retrieval costs
• Facilitated development of new applications program

   Disadvantages

• Database systems are complex, difficult, and time-consuming to design
• Substantial hardware and software start-up costs
• Damage to database affects virtually all applications program
• Extensive conversion costs in moving form a file-based system to a database system
• Initial training required for all programmers and users

9. The are three levels of abstraction: Ø Physical level: The lowest level of abstraction describes how data are stored. Ø Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data. Ø View level: The highest level of abstraction describes only part of entire database.

12.The Components of DBMS according to "Database System" a book written by Connoly-Begg are : 

·  Hardware

·  Software

·  Data

·  Procedures

·  People

DATA
Data is integrated and shared by many users.
a database is a representation of a collection of
related data.
Underlying principles: hierarchical, network,
relational or semantic.

• SOFTWARE
the components of a database management
system: data definition and data manipulation.

• USERS
application programmers, non-computer science
expert and experienced user.

• HARDWARE
consequences for the architecture of a database
system.
developments: time sharing, file server,
client/server.