DATABASE MANAGEMENT SYSTEM UNIT-I Chapter-1

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DATABASE MANAGEMENT SYSTEM
UNIT-I
Chapter-1
Introduction
Database systems have become an essential component of everyday life in modern society and
in that many frequently occurring activities involve the accessing of at least one database. e.g
in library searches, in bank transactions, in hotel/airline reservations, in grocery store
purchases, in online (Web) purchases etc.
Types of Databases and Database Applications
i) A traditional database application where most of the information is stored and
accessed is either numeric or textual.
ii) More recent applications of databases: Recent advances have led to the application
of database technology to a wider class of data:
 Multimedia Databases involving pictures, video clips, and sound
messages.
 Geographic Information Systems (GIS) involving maps, satellite images.
 Data Warehouses & on-line analytical processing (OLAP) systems are
used in many companies to extract and analyze useful information from
very large database for decision making.
 Real-time and Active Databases is used in controlling industrial and
manufacturing processes.
Definitions
Data: Data are facts that can be collected through observation & measurement such as
amount, qty, rollno, name, telephone no etc. and recorded which have some implicit meaning.
The data are organized in the form of characters, fields, record, files and databases. There are
2 types of data:
a) It is the collection of information needed by the organization.
b) Metadata - is information about the data i.e data about data.
Information: It refers to the processed data.
Knowledge: It refers to the ability to use information to achieve the desired needs/results.
Databases: The term database is a collection of all inter-related data. The major feature of
database is that the actual data are separated by the programs that use that data. A database
must have the following properties:

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 It represents some aspect of the real (or an imagined) world, called
the miniworld or Universe of Discourse (UOD). Changes to the miniworld are
reflected in the database. For example, a UNIVERSITY miniworld concerned with
students, courses, course sections, grades, and course prerequisites.
 It is a logically coherent collection of data, to which some meaning can be attached.
 It is designed, built and populated with data for a specific purpose. There is an
intended group of users and some preconceived applications in which these users are
interested.
Computerized vs. manual database
A computerized database system may be created and maintained either by a group of
application programs or by a database management systems.
A manual system on the other hand may be generated and maintained manually. E.g. the
library card catalog-based systems used in library.
Size and Complexity of the database
A database can be of any size and of varying complexity. e.g. one person's recipe database) to
being huge/complex (e.g., Amazon's database that keeps track of all its products, customers,
and suppliers).
Database Management System
Definition: A database management system (DBMS) is a collection of interrelated data and
a set of programs to access those data. Hence a DBMS is a general purpose software system
that provide an environment that is both convenient and efficient to use in each of the
following (with respect to a database):
 Defining a database: in terms of data types, structures and constraints.
 Construction: the process of storing the data on some medium (e.g., magnetic
disk) that is controlled by the DBMS.
 Manipulating the database : querying, generating reports, insertions, deletions and
modifications to its content
 Sharing: allowing multiple users and programs to access the database
"simultaneously"
 System protection: preventing database from becoming corrupted when hardware
or software failures occur
 Security protection: preventing unauthorized or malicious access to database.
A database together with the DBMS software is referred to as a database system. (See Figure
1.1, page 7.)

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Example of a Database (with a Conceptual Data Model)
1. Mini-world for the example:
a. Part of a UNIVERSITY environment.
2. Some mini-world entities:
a. STUDENTs
b. COURSEs
c. SECTIONs (of COURSEs)
d. (academic) DEPARTMENTs
3. INSTRUCTORs
Some mini-world relationships:
a. SECTIONs are of specific COURSEs
b. STUDENTs take SECTIONs
c. COURSEs have prerequisite COURSEs

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d. INSTRUCTORs teach SECTIONs
e. COURSEs are offered by DEPARTMENTs
f. STUDENTs major in DEPARTMENTs
Characteristics of the Database Approach
A number of characteristics distinguish the database approach from the traditional approach of
programming with files. In traditional file processing, each user defines and implements the
files needed for a specific software application as part of programming the application. In the
database approach, a single repository of data is maintained that is defined once and then is
accessed by various users. The main characteristics of the database approach versus the file-
processing approach are the following:
1. Self-describing nature of a database system
2. Insulation between programs and data, and data abstraction
3. Support of multiple views of the data
4. Sharing of data and multiuser transaction processing

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File Processing Systems (FPS) vs. DBMS
Characteristics File systems DBMS
1. 1.Self-
describing
nature.
In traditional file
processing system data
definition is the part of
the application program.
These programs contain
only one specific
database, whose structure
is declared in the
application program. E.g
in C program using
structure we can create a
record.
In Database Management System a single data
repository (i.e. Database) is used. So, redundancy is
reduced.
The structure and constraints of the database are
defined in the DBMS catalog. It contains the
information such as i) the structure of each file ii) the
type iii) storage format of each data item and iv)
various constraints on the data.
The information stored in the catalog is
called meta-data, and it describes the structure of the
primary database.
2. 2.Insulation
between
Programs and
Data, and Data
Abstraction
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 this
file.
Whereas in 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 and this
property is called program data independence.
Program operation independence:
In some types of database systems, such as object-
oriented an operation (also called a function or
method) is specified in two parts. The interface (or
signature) of an operation includes the operation name
and the data types of its arguments (or parameters).
The implementation (or method) of the operation is
specified separately and can be changed without
affecting the interface.
User application programs can operate on the data by
invoking these operations through their names and
arguments, regardless of how the operations are
implemented. This may be termed program-operation
independence.
Data abstraction:
The characteristic that allows program-data
independence and program-operation independence is
called data abstraction.
3. Support of
multiple views
of data
All users could see all the
data.
The DBMS may allow different users to see different
"views" of the DB, according to the perspective each
one requires.
A view may be a subset of the database or it may

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contain virtual data that is derived from the database
files but is not explicitly stored.
4. Data sharing
and
Multiuser
Transaction
Processing
Inconsistency could
result due to uncontrolled
concurrent multiuser
access.
A multiuser DBMS must allow multiple users to
access the database at the same time. This is essential
if data for multiple applications is to be integrated and
maintained in a single database.
The DBMS must include
• Concurrency control within the DBMS
guarantees that each transaction is correctly
executed or aborted.
• Recovery subsystem ensures each completed
transaction has its effect permanently recorded
in the database.
• OLTP (Online Transaction Processing) is a
major part of database applications (allows
hundreds of concurrent transactions to execute
per second)
Advantages of using a DBMS
1. Controlling Redundancy: Data redundancy means storing same data multiple
number of times (normally occurs in the "file processing" approach) leads to the
Wasted Storage Space, Duplication of effort (when multiple copies of a datum need
to be updated), and data inconsistency.
On the other hand, redundancy can be used to improve performance of queries.
Indexes, for example, are entirely redundant, but help the DBMS in processing queries
more quickly.
A DBMS should provide the capability to automatically enforce the rule that no
inconsistencies are introduced when data is updated.
2. Restricting Unauthorized Access: A DBMS should provide a security and
authorization subsystem, which is used for specifying restrictions on user accounts.
Common kinds of restrictions are to allow read-only access (no updating), or access
only to a subset of the data.
3. Providing Persistent Storage for Program Objects: Object-oriented database
systems make it easier for complex runtime objects (e.g., lists, trees) to be saved in
secondary storage so as to survive beyond program termination and to be retrievable at
a later time.
4. Permitting Inferencing and Actions Via Rules: Some database systems provide
capabilities for defining deduction rules for inferencing new information from the
stored database. Such system is called deductive database system, one may
specify declarative rules that allow the database to infer new data.

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5. Providing Multiple User Interfaces: For example, query languages for casual users,
programming language interfaces for application programmers, forms and/or
command codes for parametric users, menu-driven interfaces for stand-alone users.
6. Representing Complex Relationships Among Data: A DBMS should have the
capability to represent such relationships and to retrieve related data quickly.
7. Enforcing Integrity Constraints: Most database applications have certain integrity
constraints that must hold for data. A DBMS should provide the capabilities for
defining and enforcing these constraints. Perhaps the most fundamental constraint on a
data item is its data type, which specifies the universe of values from which its value
may be drawn. (E.g., a Grade field could be defined to be of type Grade_Type, which,
say, we have defined as including precisely the values in the set { "A", "A-", "B+", ...,
"F" }. Age field could be defined to be of type int which including the values between
18 & 65.
8. Providing Backup and Recovery: The subsystem having this responsibility ensures
that recovery is possible in the case of a system crash during execution of one or more
transactions.
Chapter-2
DDaattaa MMooddeellss,, SScchheemmaass,, aanndd IInnssttaanncceess
DDaattaa MMooddeell
 A collection of concepts that can be used to describe the structure of a
database.
 By the structure we mean the data types, relationships, and constraints that
should hold on the data.
 Also includes basic operations for specifying retrievals and updates on the
database.
 It is becoming more common to include concepts to specify the dynamic aspect
or behavior of a database application.
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aa.. CCoonncceeppttuuaall oorr hhiigghh--lleevveell
-- PPrroovviiddee ccoonncceeppttss tthhaatt aarree cclloossee ttoo tthhee wwaayy mmaannyy uusseerrss ppeerrcceeiivvee ddaattaa
((AAllssoo ccaalllleedd eennttiittyy--bbaasseedd,, oobbjjeecctt--bbaasseedd ddaattaa mmooddeellss))
- it uses concepts such as

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o entity: real-world object or concept (e.g., student, employee,
course, department, event)
o attribute: some property of interest describing an entity (e.g.,
height, age, color)
o relationship: an interaction among entities (e.g., a works-on
relationship between an employee and a project; an enrolled-in
relationship between a student and a course section)
bb.. PPhhyyssiiccaall oorr llooww--lleevveell
- Provide concepts that describe details of how data is stored in the
computer
- Meant for computer specialists, not for typical end users
cc.. IImmpplleemmeennttaattiioonn oorr rreepprreesseennttaattiioonnaall
- Provide concepts that may be understood by end users but that are not
too far removed from the way data is organized within the computer.
- Hide some details of data storage but can be implemented on a
computer system in a direct way
SScchheemmaass,, IInnssttaanncceess,, aanndd DDaattaabbaassee SSttaattee
DDaattaabbaassee SScchheemmaa ((iinntteennssiioonn))
- The description of a database.
- Not expected to change frequently.
SScchheemmaa DDiiaaggrraamm
-- AA ddiiaaggrraammmmaattiicc ddiissppllaayy ooff ((ssoommee aassppeeccttss ooff)) aa ddaattaabbaassee sscchheemmaa..
DDaattaabbaassee SSttaattee ((eexxtteennssiioonn))
- The data in the database at a particular moment of time
- Also called the current set of occurrences or instances
- Every update operation changes the database from one state to another

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Distinction between Database Schema & Database State
- The database schema changes very infrequently. The database state changes every time the
database is updated.
- Schema is also called intension. State is also called extension.
DDBBMMSS AArrcchhiitteeccttuurree aanndd DDaattaa IInnddeeppeennddeennccee
Three important DBMS characteristics of the database approach are:
- Program/data independence.
- Support of multiple views of the data.
- Use of a catalog to store the Database description.
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ttoo sseeppaarraattee uusseerr aapppplliiccaattiioonnss aanndd tthhee pphhyyssiiccaall ddaattaabbaassee.. IItt ddeeffiinneess DDBBMMSS sscchheemmaass aatt tthhrreeee
lleevveellss::
11.. IInntteerrnnaall SScchheemmaa aatt tthhee iinntteerrnnaall lleevveell
- To describes the physical storage structure and access paths —how the data
is stored.
- Uses a physical data model
22.. CCoonncceeppttuuaall SScchheemmaa aatt tthhee ccoonncceeppttuuaall lleevveell
- To describes the structure and constraints of the entire DB for all users—
what
- is stored in the DB.

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- Uses a conceptual or an implementation data model.
33.. EExxtteerrnnaall SScchheemmaa sscchheemmaass aatt tthhee eexxtteerrnnaall lleevveell
- To describe the user views.
- Typically uses the same data model as the conceptual level.
MMaappppiinnggss
- The process of transforming requests and results between levels
- Programs refer to an external schema, and are mapped by the DBMS to the
internal schema for execution.
- Data extracted from the internal DBMS level is reformatted to match the user’s
external view (e.g. formatting the results of an SQL query for display in a Web
page)
Users (including application programs) submit queries that are expressed with respect to the
external level. It is the responsibility of the DBMS to transform such a query into one that is
expressed with respect to the internal level (and to transform the result, which is at the internal
level, into its equivalent at the external level).
Example: Select students with GPA > 3.5.
Q: How is this accomplished?
A: By virtue of mappings between the levels:
external/conceptual mapping (providing logical data independence)

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conceptual/internal mapping (providing physical data independence)
DDaattaa IInnddeeppeennddeennccee iiss tthhee ccaappaacciittyy ttoo cchhaannggee tthhee sscchheemmaa aatt oonnee lleevveell ooff tthhee aarrcchhiitteeccttuurree
wwiitthhoouutt hhaavviinngg ttoo cchhaannggee tthhee sscchheemmaa aatt tthhee nneexxtt hhiigghheerr lleevveell.. TTwwoo ttyyppeess ooff ddaattaa iinnddeeppeennddeennccee
aarree ddeeffiinneedd..
11.. LLooggiiccaall DDaattaa IInnddeeppeennddeennccee
-- TThhee ccaappaacciittyy ttoo cchhaannggee tthhee ccoonncceeppttuuaall sscchheemmaa wwiitthhoouutt hhaavviinngg ttoo cchhaannggee tthhee
eexxtteerrnnaall sscchheemmaa oorr aapppplliiccaattiioonn pprrooggrraammss
22.. PPhhyyssiiccaall DDaattaa IInnddeeppeennddeennccee
-- TThhee ccaappaacciittyy ttoo cchhaannggee tthhee iinntteerrnnaall sscchheemmaa wwiitthhoouutt hhaavviinngg ttoo cchhaannggee tthhee
ccoonncceeppttuuaall sscchheemmaa
For example, the internal schema may be changed when certain file structures are reorganized
or new indexes are created to improve database performance.
When a schema at a lower level is changed, only the mappings between this schema and
higher-level schemas need to be changed in a DBMS that fully supports data independence.
The higher-level schemas themselves are unchanged. Hence, the application programs need
not be changed since they refer to the external schemas.
To understand the three-schema architecture, consider the three levels of the BOOK file
in Online Bookdatabase as shown in figure below. In this figure, two views (view 1 and view
2) of the BOOK file have been defined at the external level. Different database users can see
these views. The details of the data types are hidden from the users. At the conceptual level,
the BOOK records are described by a type definition. The application programmers and the
DBA generally work at this level of abstraction. At the internal level, the BOOK records are
described as a block of consecutive storage locations such as words or bytes. The database
users and the application programmers are not aware of these details; however, the DBA may
be aware of certain details of the physical organization of the data.

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Fig. Three levels of Online Book database (BOOK file)
The main advantage of three-schema architecture is that it provides data independence. Data
independence is the ability to change the schema at one level of the database system without
having to change the schema at the other levels. Data independence is of two types,
namely, logical data independence and physical data independence.
 Logical data independence: It is the ability to change the conceptual schema without
affecting the external schemas or application programs. The conceptual schema may
be changed due to change in constraints or addition of new data item or removal of
existing data item, etc., from the database. The separation of the external level from
the conceptual level enables the users to make changes at the conceptual level without
affecting the external level or the application programs. For example, if a new data
item, say Edition is added to the BOOK file, the two views (view 1 and view 2 shown
in above Figure are not affected.
 Physical data independence: It is the ability to change the internal schema without
affecting the conceptual or external schema. An internal schema may be changed due
to several reasons such as for creating additional access structure, changing the storage

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structure, etc. The separation of internal schema from the conceptual schema facilitates
physical data independence.
Logical data independence is more difficult to achieve than the physical data independence
because the application programs are always dependent on the logical structure of the
database. Therefore, the change in the logical structure of the database may require change in
the application programs.
AAddvvaannttaaggeess aanndd ddiissaaddvvaannttaaggeess
- The three -Schema Architecture can make it easier to achieve true data independence
- Mappings create an overhead during compilation or execution of a query or a program
- Not implemented fully by DBMSs
The database systemenvironment
The DBMS is a complex software system. The different components are as:
DBMS Component Modules
The figure is divided into two halves. The top half of the figure refers to the various users of
the database environment and their interfaces. The lower half shows the internals of the
DBMS responsible for storage of data and processing of transaction.
The database and the DBMS catalog are usually stored on disk. Access to the disk is primarily
controlled by operating system(OS).which inclues disk input/Output. A higher level stored
data manager module of DBMS controls access to DBMS information that is stored on the
disk.
If we consider the top half of the figure, it shows interfaces to DBA staff, casual users,
application programmers and parametric users.
The DDL compiler processes schema definitions, specified in the DDL, and stores the
description of the schema in the DBMS Catalog. The catalog includes information such as
names and sizes of the sizes of the files, data types of data of data items. Storage details of
each file, mapping information among schemas and constraints.
Casual users and persons with occasional need of information from database interact using
some for of interface which is interactive query interface. The queries are parsed, analysed
for correctness of the operations for the model. The names of the data elements and so on by a
query compiler that compiles them into internal form. The internal query is subjected to query
optimization..The query optimizer is concerned with rearrangement and possible recording of
operations, eliminations of redundancies.
Application programmer writes programs in host languages. The pre-compiler extracts DML
commands from an application program

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Database System Utilities
 Loading data stored in files into a database. Includes data conversion tools.
 Backing up the database periodically on tape.
 Reorganizing database file structures.
 Report generation utilities.
 Performance monitoring utilities.
 Other functions, such as sorting, user monitoring, data compression, etc.

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DATABASE MANAGEMENT SYSTEM UNIT-I Chapter-1