Module-1 Data base management systems chap1-Introduction to database.pptx

Chapter 1: Introduction to
Databases
1

Outline
 Introduction
- Basic Definitions
- Typical DBMS Functionality
- Example of a Database
 Characteristics of the Database Approach
 Advantages of Using the Database Approach
2

Introduction
 Database: A collection of related data
 Data: - Known facts
- implicit meaning
 Implicit Properties
- represents some aspect of the real world, sometimes
called the miniworld
- logically coherent collection of data with some inherent
meaning
- designed, built, and populated with data for a specific
purpose
 Database
- any size and complexity
- may be generated and maintained manually or it may
be computerized
3

 Database Management System (DBMS):
 General-purpose software system that facilitates the processes of
- Defining
- constructing
- manipulating and
- sharing databases among various users and applications.
 Functions
- protecting the database:
system protection
security protection
- maintaining it over a long period of time
Database + DBMS software = Database System
4

5
Fig: A Simplified Database System Environment

Example of a Database
 Mini-world for the example:
• UNIVERSITY database for maintaining information concerning
students, courses, and grades in a university environment
• Some mini-world entities:
1.STUDENT file: record on each student
2.COURSE file: record on each course
3.SECTION file: record on each section of a course
4.GRADE_REPORT file: stores the grades
5.PREREQUISITE file : stores the prerequisites of each course
6

Defining a UNIVERSITY database
 Specify data elements to be stored in each record
 For example:
• each STUDENT record includes data to represent the
student’s Name, Student_number, Class, Major
• each COURSE record includes data to represent the
course_name, Course_number, Credit_hours and
Department
 Specify a data type for each data element within a record
For example:
• student’s Name is a string of alphabetic characters
• student_number is an integer
7

Fig 1.2a : A database that stores student and course information
8

Fig 1.2b : A database that stores student and course information
9

Constructing the UNIVERSITY database
 store data to represent each student, course, section, grade
report, and prerequisite as a record in the appropriate file
 records in the various files may be related
 Example:
- The record for Smith in the STUDENT file is related to two
records in the GRADE_REPORT file that specify Smith’s
grades in two sections.
10

Manipulating a UNIVERSITY database
 involves querying and updating.
 Examples of queries:
• Retrieve the transcript—a list of all courses and grades—of
‘Smith’
• List the prerequisites of the ‘Database’ course
 Examples of updates :
• Create a new section for the ‘Database’ course for the
semester fall 2008
• Enter a grade of ‘A’ for ‘Smith’ in the ‘discrete mathematical
structure’ section
11

Characteristics of the Database Approach
 File Processing v/s DBMS
 Redundancy
• In traditional file processing, each user defines and implements
the files needed for a specific software application as part of
programming the application
• For example, one user, the grade reporting office, may keep
files on students and their grades
• Programs to print a student’s transcript and to enter new
grades are implemented as part of the application
• A second user, the accounting office, may keep track of
students’ fees and their payments
• Although both users are interested in data about students, each
user maintains separate files and programs to manipulate these
files because each requires some data not available from the
other user’s files
12

• Redundancy in defining and storing data results in wasted
storage space and in redundant efforts to maintain common
up-to-date data.
• In the database approach, a single repository maintains data
that is defined once and then accessed by various users.
• In file systems, each application is free to name data elements
independently.
• In contrast, in a database, the names or labels of data are
defined once, and used repeatedly by queries, transactions,
and applications.
13

Fig 1.3: Database System vs. File System
14

File System: Problem Case
15
CUSTOMER file AGENT file SALES file
A_Name (15 char)
Carol Johnson
A_Name (20 char)
Carol T. Johnson
AGENT (20 char)
Carol J. Smith
- inconsistent field name, field size
- inconsistent data values
- data duplication

 The main characteristics of the database approach versus the
file-processing approach are the following:
 Self-describing nature of a database system
 Insulation between programs and data, and data abstraction
 Support of multiple views of the data
 Sharing of data and multiuser transaction processing
16

Self-Describing Nature of a Database System
 Database system contains not only the database itself but also a
complete definition or description of the database structure and
constraints
 This definition is stored in the DBMS catalog
 The information stored in the catalog is called meta-data
 The catalog is used by the DBMS software and also by database
users who need information about the database structure
 In traditional file processing, data definition is typically part of
the application programs themselves.
 Hence, these programs are constrained to work with only one
specific database, whose structure is declared in the application
programs. 17

Insulation between Programs and Data, and Data
Abstraction
 Program-data independence
 In traditional file processing, the structure of data files is
embedded in the application programs, so any changes to the
structure of a file may require changing all programs that
access that file.
 By contrast, DBMS access programs do not require such
changes in most cases. The structure of data files is stored in
the DBMS catalog separately from the access programs.
 Program-operation independence
 Users can define operations on data as part of the database
definitions.
 User application programs can operate on the data by
invoking these operations through their names and
arguments, regardless of how the operations are
implemented.
19

 Data abstraction
 A DBMS provides users with a conceptual representation
of data that does not include many of the details of how
the data is stored or how the operations are implemented
20

Support of Multiple Views of the Data
 A database has many users, each of whom may require a
different perspective or view of the database
 A view may be a subset of the database that is derived from
the database files but is not explicitly stored
 For example, one user of the database may be interested
only in accessing and printing the transcript of each student;
the view for this user is shown in Figure below
21

Sharing of Data and Multiuser Transaction Processing
 A multiuser DBMS must allow multiple users to access the
database at the same time.
 The DBMS must include concurrency control software to
ensure that several users trying to update the same data do so
in a controlled manner so that the result of the updates is
correct.
 For example, when several reservation agents try to assign a
seat on an airline flight, the DBMS should ensure that each seat
can be accessed by only one agent at a time for assignment to a
passenger.
22

Advantages of Using the DBMS Approach
1. Controlling Redundancy
2. Restricting Unauthorized Access
3. Providing Persistent Storage for Program Objects
4. Providing Storage Structures and Search Techniques for
Efficient Query Processing
5. Providing Backup and Recovery
6. Providing Multiple User Interfaces
7. Representing Complex Relationships among Data
8. Enforcing Integrity Constraints
9. Permitting Inferencing and Actions Using Rules
10.Additional Implications of Using the Database Approach
23

Advantages of Using the DBMS Approach
1. Controlling Redundancy
 Redundancy leads to several problems- duplication, wastage
of storage and data may become inconsistent.
 In the database approach, the views of different user groups
are integrated during database design.
 Database design that stores each logical data item in only one
place in the database. This is known as data normalization,
and it ensures consistency and saves storage space
24

 It is sometimes necessary to use controlled redundancy to
improve the performance of queries
 For example, we may store Student_name and Course_number
redundantly in a GRADE_REPORT file because whenever we
retrieve a GRADE_REPORT record, we want to retrieve the
student name and course number along with the grade,
student number, and section identifier.
 By placing all the data together, we do not have to search
multiple files to collect this data. This is known as
denormalization.
25

2.Restricting Unauthorized Access
 When multiple users share a large database, it is likely that
most users will not be authorized to access all information in
the database.
 For example, financial data is often considered confidential, and
only authorized persons are allowed to access such data.
 A DBMS should provide a security and authorization
subsystem, which the DBA uses to create accounts and to
specify account restrictions
 DBMS should enforce these restrictions automatically
26

3. Providing Persistent Storage for Program Objects
 object-oriented database systems make it easier for complex
runtime objects to be saved in secondary storage so as to
survive beyond program termination and to be retrievable at a
later time.
 Object-oriented database systems are compatible with
programming languages such as C++ and Java, and the DBMS
software automatically performs any necessary conversions.
27

4. Providing Storage Structures and Search Techniques for
Efficient Query Processing
 The DBMS maintains indexes that are utilized to improve the
execution time of queries and updates.
 DBMS has a buffering or caching module that maintains parts of
the database in main memory buffers.
 The query processing and optimization module is responsible
for choosing an efficient query execution plan for each query
submitted to the system
28

5. Providing Backup and Recovery
 The backup and recovery subsystem of the DBMS is
responsible for recovery.
 ensures that recovery is possible in the case of a system crash
during execution of one or more transactions.
 Disk backup is also necessary in case of a catastrophic disk
failure.
29

6 Providing Multiple User Interfaces
 Because many types of users with varying levels of technical
knowledge use a database, a DBMS should provide a variety of
user interfaces.
 These include
- query languages for casual users
- programming language interfaces for application
programmers
- forms and command codes for parametric users
- menu-driven interfaces and natural language interfaces
for standalone users.
30

7. Representing Complex Relationships among Data
 A database may include numerous varieties of data that are
interrelated in many ways.
 For example each section record is related to one course
record and to a number of GRADE_REPORT records—one for
each student who completed that section.
 A DBMS must have the capability to represent a variety of
complex relationships among the data, to define new
relationships as they arise, and to retrieve and update related
data easily and efficiently.
31

8.Enforcing Integrity Constraints
 Most database applications are such that the semantics of the
data require that it satisfy certain restrictions in order to make
sense.
 The simplest type of integrity constraint involves specifying a
data type for each data item.
- For example, in student table we specified that the value of
Name must be a string of no more than 30 alphabetic
characters.
 More complex type of constraint is referential integrity involves
specifying that a record in one file must be related to records in
other files
- For example, in university database, we can specify that
every section record must be related to a course record.
32

 Another type of constraint specifies uniqueness on data item
values, such as every course record must have a unique value
for Course_number. This is known as a key or uniqueness
constraint.
 It is the responsibility of the database designers to identify
integrity constraints during database design.
33

9.Permitting Inferencing and Actions Using Rules
 In a deductive database system, one may specify declarative
rules that allow the database to infer new data.
 For example figure out which students are on academic
probation.
 These can be specified declaratively as rules, which when
compiled and maintained by the DBMS
 In today’s relational database systems, it is possible to
associate triggers with tables.
 A trigger is a form of a rule activated by updates to the table
 Stored procedures
- More involved procedures to enforce rules
34

10 Additional Implications of Using the Database Approach
 Potential for Enforcing Standards
- permits the DBA to define and enforce standards among
database users in a large organization which facilitates
communication and cooperation among various
departments, projects, and users within the organization.
- Standards can be defined for names and formats of data
elements, display formats, report structures and so on.
 Reduced Application Development Time
- once a database is up and running, substantially less time is
generally required to create new applications using DBMS
facilities
35

 Flexibility
- It may be necessary to change the structure of a database as
requirements change.
- DBMSs allow changes to the structure of the database without
affecting the stored data and the existing application programs.
 Availability of Up-to-Date Information
- DBMS makes the database available to all users
- availability of up-to-date information is essential for many
transaction-processing applications, such as reservation systems
or banking databases
36

 Economies of Scale
- DBMS approach permits consolidation of data and
applications, to overlap between activities of data-processing
in different projects or departments
- enables the whole organization to invest in more powerful
processors, storage devices, or communication gear, rather
than having each department purchase its equipment.
-reduces overall costs of operation and management.
37

Question Bank
1. Define database and briefly explain the implicit properties
of the database.
2. Discuss the main Characteristics of the database
approach and how does it differ from Traditional file
systems?
3. Define Database Management System. Briefly discuss
the advantages of using the DBMS.
38

Module-1 Data base management systems chap1-Introduction to database.pptx

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Module-1 Data base management systems chap1-Introduction to database.pptx