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Database Management Systems

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Database Management System (CS403)
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Lecture No. 02
Reading Material
"Database Systems Principles, Design and Implementation"
written by Catherine Ricardo, Maxwell Macmillan.
Overview of Lecture
o Some Additional Advantages of Database Systems
o Costs involved in Database systems
o Levels of data
o Database users
Difference between Data and Information
Data is the collection of raw facts collected from any specific environment for a specific
purpose. Data in itself does not show anything about its environment, so to get desired
types of results from the data we transform it into information by applying certain
processing on it. Once we have processed data using different methods data is converted
into meaningful form and that form of the Data is called information
Example:
Example:
Fig. 1: Data and Information
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If we consider the data in the above figure without the titles or the labels associated with
the data (EmpName, age, salary) then it is not much useful. However, after attaching
these labels it brings some meanings to us, this meaningfulness is further increased when
we associate some other labels, like the company name and the department name etc. So
this is a very simple example of processing that we can do on the data to make it
information.
Once we have clear idea of what data and information is we proceed with another term
knows as "schema" Schema is a repository or structure to express the format and other
different information about data and database, as we can see from the database definition
"Database is a self describing collection of interrelated records." The word self
describing means that the data storage and retrieval mechanism and its format is
described in the database, Actual place where these definitions and descriptions are
performed is database schema.
o Database Application:
Database Application is a program or group of programs which is used for performing
certain operations on the data stored in the database. These operations may contain
insertion of data into a database or extracting some data from the database based on a
certain condition, updating data in the database, producing the data as output on any
device such as Screen, disk or printer.
o Database Management Systems:
Database management system is software of collection of small programs to perform
certain operation on data and manage the data.
Two basic operations performed by the DBMS are:
·
Management of Data in the Database
Management of Users associated with the database.
·
Management of the data means to specify that how data will be stored, structured and
accessed in the database.
Management of database users means to manage the users in such a way that they can
perform any desired operations on the database. DBMS also ensures that a user can not
perform any operation for which he is not allowed. And also an authorized user is not
allowed to perform any action which is restricted to that user.
In General DBMS is a collection of Programs performing all necessary actions associated
to a database.
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Further Advantages of Database Systems:
Database systems are very much beneficent to enterprises and businesses, some of the
advantages are listed below:
o Data consistency
o Better data security
o Faster development of new applications
o Economy of scale
o Better concurrency control
o Better backup and recovery procedures
o Data Consistency:
Data consistency means that the changes made to different occurrence of data should be
controlled and managed in such a way that all the occurrences have same value for any
specific data item. Data inconsistency leads to a number of problems, including loss of
information and incorrect results. In database approach it is controlled because data is
shared and consistency is controlled and maintained.
o Better Data Security:
All application programs access data through DBMS, So DBMS can very efficiently
check that which user is performing which action and accessing which part of data , So A
DBMS is the most effectively control and maintain security of Data stored in a database.
o Faster Application Development:
The database environment allows us faster application development because of its many
reasons. As we know that database is designed with the factor of future development in
mind
So whenever we have to build a new application to meet the growing needs of the
computerized environment, it may be easy due to the following reason:
The data needed for the new application already resides in the database.
·
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·
The data might not already reside in the database but it could be derived
from the data present in the database
Thus we can say that, to develop a new application for an existing database system less
effort is required in terms of the system and database design.
o Economy of Scale:
Databases and database systems are designed to share data stored in one location for
many different purposes, So it needs not be stored as many number of times in different
forms as it is used, for example the data used by Admission Department of any education
institution can be used to maintain the attendance record of the students as well as the
examination records of the students. So it saves us lots of efforts and finances providing
economy of scale.
o Better Concurrency Control:
Concurrency means the access of database form as number of points simultaneously.
Concurrency control means to access the database in such a way that all the data accesses
are completed correctly and transparently. One example of controlled concurrency is the
use of ATM Machine for withdrawal of money (cash). All ATM machines of a bank are
interconnected to a central database system worldwide, so that a user can access its
account from anywhere in the world and can get cash from any ATM terminal. As there
are thousands of ATM terminal across the world for a specific bank so as a result
thousands of user process and access the bank's database. All this process is managed
concurrently using the database systems and is done in such an efficient manner that no
two user face any delay in the processing of their requests.
o Better Backup and Recovery Facility:
Data is a very important resource and is very much valuable for any organization, loss of
such a valuable resource can result in a huge strategic disasters. As Data is stored on
today's' storage devices like hard disks etc., It is necessary to take periodic backups of
data so that in case a storage device looses the data due to any damage we should be able
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to restore the data a nearest point, Database systems offer excellent facilities for taking
backup of data and good mechanism of restoring those backups to get back the backed-up
data.
It some time happens that a database which was in use and very important transactions
were made after the last backup was made, all of a sudden due to any disastrous situation
the database crashes (improper shutdown, invalid disk access, etc.) Now in such a
situation the database management system should be able to recover the database to a
consistent state so that the transactions made after the last backup are not lost.
Cost Involved:
Enjoying all these benefits of the database systems do have some additional costs on any
organization which is going to adopt a database environment. These charges may also be
known as the disadvantages of the database system. Different types of costs (Financial
and Personnel) which an organization faces in adopting a database system are listed
below:
o High Cost:
Database Systems have a number of inherent charges which are to be born by any
organization that is going to adopt it. High Cost is one of these inherent charges, it
includes the need for specialized software which is used to run database systems,
Additional and specialized hardware and technically qualified staff are the requirements
for adopting to the database system, all these requirements need an organization to invest
handsome amount of money to have all the requirements of the database systems.
o Conversion Cost:
Once an organization has decided to adopt database system for its operations, it is not
only the finance and technical man-power which is required for switching on to database
system, it further has some conversion charges needed for adopting the database system,
this is also a very important stage for making decision about the way the system will be
converted to database system.
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o Difficult Recovery Procedures:
Although the database systems and database management systems provide very efficient
ways of data recovery in case of any disaster, still the process of recovering a crashed
database is very much technical and needs good professional skills to perform a perfect
recovery of the database.
Importance of Data
o Data as a Resource:
A resource is anything which is valuable for an organization. There can be a number of
resources in any organization, for example, Buildings, Furniture, Vehicle, Technical Staff,
Managers, supporting staff and Machinery etc. As all these are resources for
organizations and are consumed very much carefully to get full benefit out of them, Data
in the same way is a very important resources and needs to considered equally important
as other resource are considered.
Why we call data as a resource?
Data is truly considered a resource because for an organization to make proper decisions
at proper time it is only the data which can provide correct information and in-turn cause
good utilization of other organizational resources. Organizations can not make good and
effective decisions if the required data is not available in time or in the correct and
desired format, such bad and miscalculated decisions ultimately lead to the failure of
organizations or business.
Levels of Data
o Real World Data
The real world level of data means that level of data at which entities or objects exist in
reality, it means that any object existing in reality have a name and other identifiable
attributes through which we can identify that specific object or entity.
Example:
Any Student
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o Meta Data:
For storage of the data related to any entity or object existing at real world level we
define the way the data will be stored in the database. This is called Meta data. Meta data
is also known as schema for the real world data. It tells that what type of data will be
stored in the database what will be size of a certain attribute of the real world data, how
many and what attributes will be used to store the data about the entity in the database.
Example:
Name , Character Type, 25 character size field,
Age,
Date type,
8 bytes size
Class,
Alpha Numeric,
8 byte size field
o Existence of Data:
Existence of the data level shows the actual data regarding the entities as real world level
according to the rules define at the Meta Data level.
Example:
According to the definition given in the Meta data level the Actual data or Data
occurance for the entity at real world level is shown below:
Name Age
Class
Ali
20/8/1979
MCS-I
Amir
22/3/1978
MCS-II
etc...
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Fig. 2: Levels of Data
Users of Database Systems:
o Application Programmers
o End Users
Naïve
·
Sophisticated
·
o Application programmers:
This category of database users contains those people who create different types of
database application programs that we have seen earlier. Application programmers design
the application according to the needs of the other users of the database in a certain
environment. Application programmers are skilled people who have clear idea of the
structure of the database and know clearly about the needs of the organizations.
o End Users:
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Second category of the Database users are the end users, this group of users contains the
people who use the database application programs developed by the Application
programmers. This category further contains two types of users
Naïve Users
·
Sophisticated Users
·
Naïve Users
·
This category of users is that category who simply use the application database programs
created by the programmers. This groups has no interaction with other parts of there
database and only use the programs meant for them. They have not to worry about the
further working of the database.
Sophisticated Users:
·
This type of users has some additional rights over the Naïve users, which means that they
can access the data stored in the database any of their desired way. They can access data
using the application programs as well as other ways of accessing data. Although this
type of users has more rights to access data, but these users have to take more
responsibility and they need to be aware of the database structure. Moreover such users
should be skilled enough to be able to get data from database with making and damage or
loss to the data in database.
o Database Administrators (DBA):
This class of database users is the most technical class of db users. They need to have the
knowledge of how to design and manage the database use as well as to manage the data
in the database. DBA is a very responsible position in an organization. He is responsible
for proper working of the database and DBMS, has the responsibility of making proper
database backups and make necessary actions for recovering the database in case of a
database crash. To fulfill the requirements of a DBA position a DBA needs vast
experience and very elegant technical skills.
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·  Duties of the DBA
A Database administrator has some very precisely defined duties which need be
performed by the DBA very religiously. A short account of these jobs is listed below:
o Schema definition
o Granting data access
o Routine Maintenance
·
Backups
·
Monitoring disk space
·
Monitoring jobs running
o Schema Design
DBA in some organization is responsible for designing the database schema, which
means that DBA is the person who create all the meta Data information for the
organization on which the database is based. However in some very large scale
organizations this job is performed by the Database designer, which is hired for the
purpose of database Design and once the database system, is installed and working it is
handed over to the DBA for further operation.
o Granting Access to Users:
DBA is also responsible for grant of access rights to the database users. Along with
granting and revoking (taking back) the rights the DBA continuously monitors and ensure
the legal use of these rights.
o Monitoring Disk Space :
When a new database is created it takes a limited space but as a result of daily activity the
database acquires more data and grows in size very rapidly. The DBA has to monitor the
disk space usage and statistics to ensure that no data over flow occurs at any stage.
o Monitoring Running Jobs:
To ensure the secure and proper functioning of the database system a DBA continuously
monitors some associated activities also and ensure that all users are using their
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authorities legally and different devices attached to the database system are functioning
properly.
Typical Components of a Database Environment:
Different typical components of a database environment are shown in the figures below;
they describe graphically the role of different types of users.
Fig. 3: DBMS and Database
Database is used to store data and DBMS uses mechanisms to get data from the database
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Fig. 4: Application Programs
Application programs talk to DBMS and ask for the data required
Fig. 5: Database Designers
Database designers design (for large organizations) the database and install the DBMS
for use by the users of the database in any specific organization.
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Fig. 6: Database Administrator
Once Database has been installed and is functioning properly in a production
environment of an organization the Database Administrator takes over the charge and
performs specific DBA related activities including:
o Database maintenance.
o Database Backup.
o Grant of rights to database users.
o Monitoring of Running Jobs
o Managing Print jobs
o Ensuring quality of Service to all users.
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Fig. 7: Database Administration's interaction with other users
o Database administrator can interact with the database designer during database
design phase so that he has a clear idea of the database structure for easy
reference in future.
o This helps DBA perform different tasks related to the database structure.
o DBA also interacts with the application programmers during the application
development process and provides his services for better design of applications.
o End users also interact with the system using application programs and other tools
as specified in the description above.
This concludes lecture number 2, in case of any queries, please feel free to contact.
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Table of Contents:
  1. Introduction to Databases and Traditional File Processing Systems
  2. Advantages, Cost, Importance, Levels, Users of Database Systems
  3. Database Architecture: Level, Schema, Model, Conceptual or Logical View:
  4. Internal or Physical View of Schema, Data Independence, Funct ions of DBMS
  5. Database Development Process, Tools, Data Flow Diagrams, Types of DFD
  6. Data Flow Diagram, Data Dictionary, Database Design, Data Model
  7. Entity-Relationship Data Model, Classification of entity types, Attributes
  8. Attributes, The Keys
  9. Relationships:Types of Relationships in databases
  10. Dependencies, Enhancements in E-R Data Model. Super-type and Subtypes
  11. Inheritance Is, Super types and Subtypes, Constraints, Completeness Constraint, Disjointness Constraint, Subtype Discriminator
  12. Steps in the Study of system
  13. Conceptual, Logical Database Design, Relationships and Cardinalities in between Entities
  14. Relational Data Model, Mathematical Relations, Database Relations
  15. Database and Math Relations, Degree of a Relation
  16. Mapping Relationships, Binary, Unary Relationship, Data Manipulation Languages, Relational Algebra
  17. The Project Operator
  18. Types of Joins: Theta Join, Equi–Join, Natural Join, Outer Join, Semi Join
  19. Functional Dependency, Inference Rules, Normal Forms
  20. Second, Third Normal Form, Boyce - Codd Normal Form, Higher Normal Forms
  21. Normalization Summary, Example, Physical Database Design
  22. Physical Database Design: DESIGNING FIELDS, CODING AND COMPRESSION TECHNIQUES
  23. Physical Record and De-normalization, Partitioning
  24. Vertical Partitioning, Replication, MS SQL Server
  25. Rules of SQL Format, Data Types in SQL Server
  26. Categories of SQL Commands,
  27. Alter Table Statement
  28. Select Statement, Attribute Allias
  29. Data Manipulation Language
  30. ORDER BY Clause, Functions in SQL, GROUP BY Clause, HAVING Clause, Cartesian Product
  31. Inner Join, Outer Join, Semi Join, Self Join, Subquery,
  32. Application Programs, User Interface, Forms, Tips for User Friendly Interface
  33. Designing Input Form, Arranging Form, Adding Command Buttons
  34. Data Storage Concepts, Physical Storage Media, Memory Hierarchy
  35. File Organizations: Hashing Algorithm, Collision Handling
  36. Hashing, Hash Functions, Hashed Access Characteristics, Mapping functions, Open addressing
  37. Index Classification
  38. Ordered, Dense, Sparse, Multi-Level Indices, Clustered, Non-clustered Indexes
  39. Views, Data Independence, Security, Vertical and Horizontal Subset of a Table
  40. Materialized View, Simple Views, Complex View, Dynamic Views
  41. Updating Multiple Tables, Transaction Management
  42. Transactions and Schedules, Concurrent Execution, Serializability, Lock-Based Concurrency Control, Deadlocks
  43. Incremental Log with Deferred, Immediate Updates, Concurrency Control
  44. Serial Execution, Serializability, Locking, Inconsistent Analysis
  45. Locking Idea, DeadLock Handling, Deadlock Resolution, Timestamping rules