15-05-2013, 03:24 PM
Database Systems
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Introduction
What is a Database?
A collection of related pieces of data:
Representing/capturing the information about a real-world enterprise or part of an enterprise.
Collected and maintained to serve specific data management needs of the enterprise.
Activities of the enterprise are supported by the database andcontinually update the database.
Database Management System (DBMS)
A general purposesoftware system enabling:
Creation of large disk-resident databases.
Posing of data retrieval queries in a standard manner.
Retrieval of query results efficiently.
Concurrent use of the system by a large number of users in a consistent manner.
Guaranteed availability of data irrespective of system failures.
OS File System
Storage Based Approach
•Files of records –used for data storage
•data redundancy –wastage of space
•maintaining consistency becomes difficult
•Record structures –hard coded into the programs
•structure modifications –hard to perform
•Each different data access request (a query)
•performed by a separate program
•difficult to anticipate all such requests
•Creating the system
•requires a lot of effort
•Managing concurrent access and failure recovery are difficult