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					                           CS203–Database Management Systems
                                    Lecture 1- Summary

What is a Database?
  • Collection of related data organized to facilitate retrieval, management and updating
          o Data – known facts that can be recorded and that have implicit meaning

   •   Properties
          o Represents some aspects of the real world – miniworld (UoD)
                   Changes in UoD are reflected in the database
          o Logically coherent collection of data with inherent meaning
          o Designed, built and populated for some specific purpose
                   Intended user group
                   Set of applications

Database Management System(DBMS)
   • A collection of programs that enables a user to create and maintain the database
         o Defining
                 Specifying the types of data, structures, constraints
         o Constructing
                 Storing the data on a storage medium
         o Manipulating
                 Retrieving specific data , updating , generating reports

DBMS classification
  • Data model
        o Relational
        o Object
        o Hierarchical
        o Network
                  Most commonly used- relational model

   •   Number of users
         o Single user
                  Only one user at a given time
         o Multi-user
                  Supports multiple users at the same time

   •   Number of cites over which the database is distributed
         o Centralized
                  Stored at a single site
         o Distributed
                  Distributed over many sites connected by a network

   •   General purpose
          o Can be used for various applications
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   •   Special purpose
          o Built for specific application
                   Air line reservations
                         Large number of concurrent transactions need to be performed
                            without delays

Database system
   • A database system is a combination of the database and the DBMS

Characteristics of database approach
   • In the conventional file processing environment, each user defines, and implements his
      own files for specific applications
          o Two level architecture, consisting of the user level and the machine level with the
              translator and operating system interfacing between the two levels
   • In database approach
          o Single repository of data
          o Accessed by many users
   • Characteristics
          o Self describing nature
          o Program-data independence, program operation independence
          o Support for multiple views
          o Multiuser transaction processing
Database transactions
   • Database transactions have the following properties:
          o Atomicity: A transaction is an atomic unit of processing: it is either performed in
              its entirety or not performed at all.
          o Isolation: Transactions that execute concurrently should not interfere with each
              other; so each transaction appears as though it is executed in isolation
          o Consistency Preservation: The execution of a transaction should take the database
              from one consistent state to another
          o Durability or Permanency: The changes committed in a database must not be lost
              as a result of any failure. They must persist in the database

Advantages of a DBMS
   • Controlling redundancy
   • Restricting unauthorized access
   • Providing multiple user interfaces
   • Providing backup and recovery
   • Providing Storage Structures for Efficient Query Processing
   • Representing Complex Relationships among Data
   • Enforcing integrity constraints
Participants of a DBMS
Database Administrators
   • The database administrator (DBA) is a person (or group of persons) responsible for the
       overall control of the entire database system. Specifically, the DBA does the following:

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           o   Deciding on the information content of the database.
           o   Deciding on the storage structure and access strategy.
           o   Defining strategy for backup and recovery.
           o   Defining authorization checks and validation procedures.
           o   Liaising with users.
           o   Acquiring necessary software and hardware resources.
           o   Monitoring performance and responding to changes in requirements.

Database Designers

   •   The database designers are responsible for defining the content, the structure, the
       constraints, and functions or transactions against the database.
   •   They must communicate with the end-users and understand their needs.

Software Engineers

   •   This includes systems analysts and application programmers.
   •   System analysts determine requirements of end users and design canned transactions that
       meet these requirements.
   •   Application programmers implement these specifications as programs.

End users
   • The end users basically use the database for queries, reports and some of them actually
       update the database content
   • Categories
       • Casual end users
          Occasionally access the database
              o May access different information each time
              o Use a query language
                       E.g. Middle of high-level managers

       •   Parametric end users
              o Query and update the database constantly
              o Use standard types of queries and updates
                   Carefully programmed and tested
       •   Sophisticated end users
              o Have complex requirements
              o Get to know the facilities of the DBMS well to get their requirements

       •   Stand-alone end users
              o Maintain personal databases
              o Use ready-made program packages




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