unit 1.pdf

4
Basic Definitions
• Database: A collection of related data.
• Data: Known facts that can be recorded and have an
implicit meaning.
• Database Management System (DBMS): A software
package/ system to facilitate the creation and
maintenance of a computerized database.
• Database System: The DBMS software together with
the data itself. Sometimes, the applications are also
included.

• SQL/SQL+/SQLServer/MySQL
• Database System/ File System
• Applications/ Advantages of DBMS
• Anomalies/ redundancy
• Types of Database
• Architecture:
– Data Abstraction/ Application/ Overall (Components Based)
• Physical/ Logical Independence
• Database Users
• Schema/ Instance
• DDL/DML/DCL
• Procedural/ Non Procedural DML
• DBMS/RDBMS
• Char/varchar/varchar2/nchar/nvarchar
• XML

Difference Between File and DBMS Operations

Difference Between File and DBMS
Database Management System
File Management System
Database management system is used when
security constraints are high.
File System is a general, easy-to-use system to
store general files which require less security
and constraints.
Data Redundancy is less in database management
system.
Data Redundancy is more in file management
system.
Data Inconsistency is less in database management
system.
Data Inconsistency is more in file system.
Centralisation is achieved in Database Management
System.
Centralisation is hard to get when it comes to
File Management System.
In Database Management System, user is unaware
of physical address where data is stored.
User locates the physical address of the files to
access data in File Management System.
Security is high in Database Management System.
Security is low in File Management System.
Database Management System stores structured
data which have well defined constraints and
interrelation.
File Management System stores unstructured
data as isolated data files/entities.

Advantages of DBMS
1. Controlling Redundancy:
2. Integrity can be enforced: Integrity of data means that data in
database is always accurate
3. Inconsistency can be avoided : When the same data is duplicated
and changes are made at one site, which is not propagated to the
other site, it gives rise to inconsistency and the two entries regarding
the same data will not agree.
4. Data can be shared
5. Standards can be enforced
6. Restricting unauthorized access
7. Providing Backup and Recovery
8. Data Model can be developed
9. Concurrency Control

Disadvantages of DBMS
• 1. Complexity
• 2. Size
• 3. Performance
• 4. Higher impact of a failure
• 5. Cost of DBMS
• 6. Additional Hardware costs

Database Application Architectures
Old Modern

Database Application Architectures

Three-Tier Architecture
• A 3-tier application is an application program that
is organized into three major parts, comprising of
data access layer tier at the bottom, the
application tier (business logic) in the middle and
the client tier (Presentation) at the top and each
tier is distributed to a different place or places in
a network.
1. Presentation Layer (UI)
2. Business Logic Layer
3. Data Access Layer

• User (Presentation) Tier − End-users operate on this tier and they
know nothing about any existence of the database beyond this
layer. At this layer, multiple views of the database can be provided
by the application. All views are generated by applications that
reside in the application tier.
• Application (Middle/Business) Tier − At this tier reside the
application server and the programs that access the database. For a
user, this application tier presents an abstracted view of the
database. End-users are unaware of any existence of the database
beyond the application. At the other end, the database tier is not
aware of any other user beyond the application tier. Hence, the
application layer sits in the middle and acts as a mediator between
the end-user and the database.
• Database (Data) Tier − At this tier, the database resides along with
its query processing languages. We also have the relations that
define the data and their constraints at this level.

• Presentation Layer (UI)
– This layer presents data to the user and optionally permits data
manipulation and data entry, also this layer requests the data form
Business layer.
– This layer accomplished through use of Dynamic HTML and client-side
data sources and data cursors.
• Business Logic Layer
– The business logic acts as the server for client requests from
workstations.
– It acts according Business rules fetch or insert data through the Data
Layer.
– In turn, it determines what data is needed (and where it is located)
and acts as a client in relation to a third tier of programming that
might be located on a local or mainframe computer.
– Because these middle-tier components are not tied to a specific client,
they can be used by all applications and can be moved to different
locations, as response time and other rules require.
• Data Access Layer

• Presentation Layer (UI)
• Business Logic Layer
• Data Access Layer
– The third tier of the 3-tier system is made up of the
DBMS that provides all of the data for the above two
layers.
– This is the actual DBMS access layer.
– Avoiding dependencies on the storage mechanisms
allows for updates or changes without the application
tier clients being affected by or even aware of the
change.

Three Level Architecture of DBMS

20
View 1
Item_Name
Price
Conceptual
Item_Number Character (6)
Item_Name Character(30)
Price Numeric(5,2)
Stock Numeric(4)
Physical
Stored_Item Length=50
Item # Type = Byte(6), offset = 0, Index = Ix
Name Type = Byte(30), offset = 6
Price Type = Byte(8), offset = 36
Stock Type = Byte(4), offset = 44
External
(View)
Level
Conceptual
(Logical)
Level
Physical
Level
View 2
Item_Name
Stock
Sales Officer Inventory Controller

• Physical Level:
– At physical level, the information about location of
database objects in data store is kept.
– Various users are DBMS are unaware about the locations
of these objects.
• Conceptual (Logical) Level
– Data is represented in the form of various database
tables.
– For Example, STUDENT database may contain STUDENT
and COURSE tables which will be visible to users but
users are unaware about their storage.
• External (View) Level

• Physical Level:
• Conceptual (Logical) Level:
• External (View) Level:
– specifies a view of the data in terms of conceptual level
tables.
– Each external level view is used to cater the needs of a
particular category of users.
– For Example, FACULTY of a university is interested in
looking course details of students, STUDENTS are
interested in looking all details related to academics,
accounts, courses and hostel details as well.
– Different views can be generated for different users.

Data Independence
• Data independence means change of data at
one level should not affect another level. Two
types of data independence are required in
this architecture:
– Physical Data Independence:
– Conceptual Data Independence:

Data Independence
• Physical Data Independence:
– Any change in physical location of tables and
indexes should not affect conceptual level or
external view of data.
– This data independence is easy to achieve and
implemented by most of the DBMS.
• Conceptual Data Independence

Data Independence
• Physical Data Independence
• Conceptual Data Independence:
– The data at conceptual level schema and external
level schema must be independent.
– This means, change in conceptual schema should not
affect external schema.
– Adding or deleting attributes of a table should not
affect the user’s view of table.
– But this type of independence is difficult to achieve as
compared to physical data independence because the
changes in conceptual schema are reflected in user’s
view.

Phases of database design
• Database designing for a real world application starts from
capturing the requirements to physical implementation
using DBMS software which consists of following steps
• Conceptual Design: The requirements of database are
captured using high level conceptual data model. For
Example, ER model is used for conceptual design of
database.
• Logical Design: Logical Design represents data in the form
of relational model. ER diagram produced in conceptual
design phase is used to convert the data into Relational
Model.
• Physical Design: In physical design, data in relational model
is implemented using commercial DBMS like Oracle, DB2.

What Is a Data Dictionary?
• Contains information about the structures in the
database
• Also called
– System Catalog
• Strictly speaking this is what Oracle has
– Meta Data
• Generic term, for data about data
– Data Repository
• Synonym for Data Dictionary used to imply stand-alone systems
• According to Codd an RDB MUST use tables for its
Data Dictionary

31
Database Users
• Database administrators: responsible for authorizing access
to the database, for co-ordinating and monitoring its use,
acquiring software, and hardware resources, controlling its
use and monitoring efficiency of operations.
• Database Designers: responsible to define the content, the
structure, the constraints, and functions or transactions
against the database. They must communicate with the end-
users and understand their needs.
• End-users: they use the data for queries, reports and some of
them actually update the database content.
– Naïve or Parametric : they make up a large section of the end-user
population. They use previously well-defined functions in the form
of “canned transactions” against the database. Examples are bank-
tellers or reservation clerks who do this activity for an entire shift of
operations.
– Sophisticated : these include business analysts, scientists,
engineers, others thoroughly familiar with the system capabilities.
Many use tools in the form of software packages that work closely
with the stored database.

12 Rules By Dr. Codd
• Rule 1: Information Rule
– The data stored in a database, may it be user data or metadata,
must be a value of some table cell. Everything in a database
must be stored in a table format.
• Rule 2: Guaranteed Access Rule
– Every single data element (value) is guaranteed to be accessible
logically with a combination of table-name, primary-key (row
value), and attribute-name (column value). No other means,
such as pointers, can be used to access data.
• Rule 3: Systematic Treatment of NULL Values
– The NULL values in a database must be given a systematic and
uniform treatment. This is a very important rule because a NULL
can be interpreted as one the following − data is missing, data is
not known, or data is not applicable.

• Rule 4: Active Online Catalog
– The structure description of the entire database must be stored
in an online catalog, known as data dictionary, which can be
accessed by authorized users. Users can use the same query
language to access the catalog which they use to access the
database itself.
• Rule 5: Comprehensive Data Sub-Language Rule
– A database can only be accessed using a language having linear
syntax that supports data definition, data manipulation, and
transaction management operations. This language can be used
directly or by means of some application. If the database allows
access to data without any help of this language, then it is
considered as a violation.
• Rule 6: View Updating Rule
– All the views of a database, which can theoretically be updated,
must also be updatable by the system.

• Rule 7: High-Level Insert, Update, and Delete Rule
– A database must support high-level insertion, updation, and
deletion. This must not be limited to a single row, that is, it must
also support union, intersection and minus operations to yield
sets of data records.
• Rule 8: Physical Data Independence
– The data stored in a database must be independent of the
applications that access the database. Any change in the
physical structure of a database must not have any impact on
how the data is being accessed by external applications.
• Rule 9: Logical Data Independence
– The logical data in a database must be independent of its user’s
view (application). Any change in logical data must not affect the
applications using it. For example, if two tables are merged or
one is split into two different tables, there should be no impact
or change on the user application. This is one of the most
difficult rule to apply.

• Rule 10: Integrity Independence
– A database must be independent of the application that uses it.
All its integrity constraints can be independently modified
without the need of any change in the application. This rule
makes a database independent of the front-end application and
its interface.
• Rule 11: Distribution Independence
– The end-user must not be able to see that the data is
distributed over various locations. Users should always get the
impression that the data is located at one site only. This rule has
been regarded as the foundation of distributed database
systems.
• Rule 12: Non-Subversion Rule
– If a system has an interface that provides access to low-level
records, then the interface must not be able to subvert the
system and bypass security and integrity constraints.

DBMS Vs RDBMS
37
RDBMS
DBMS
Relationship between two tables or files
can be specified at the time of table
creation
Relationship between two files or tables
maintain programmatically
Supports client/server architecture
Does not support client/server architecture
Supports Distributed Databases
Does not support Distributed database
Multilevel security
1. Logging in at OS level
2. Command level
3. Object level
No security of Data
1. RDBMS usually satisfy more than 7 or 8
rules of E.F. Codd
DBMS may satisfy less than 7 or 8 rules of
E.F. Codd

38
Basic Definitions
• Database: A collection of related data.
• Data: Known facts that can be recorded and have an
implicit meaning.
• Database Management System (DBMS): A software
package/ system to facilitate the creation and
maintenance of a computerized database.
• Database System: The DBMS software together with
the data itself. Sometimes, the applications are also
included.

XML: Extensible Markup Language
• Originally intended as a document markup
language not a database language
• The ability to specify new tags, and to
create nested tag structures made XML a
great way to exchange data, not just
documents
• XML has become the basis for all new
generation data interchange formats.
• A wide variety of tools is available for
parsing, browsing and querying XML
documents/data

Questions for reference.
• What is the concept of data independence and explain its importance in
database environment.
– Explain Physical level and Logical level of abstraction.
• What do you mean by database management system? Explain its
advantages/ disadvantages over file system.
– how is it possible to get more information from the same amount of data by
using a database approach as opposed to a file approach.
• Give the roles of database administrator and data base designer.
• Define Schema and Instance.
• Define redundancy. Can data redundancy be completely eliminated when
database approach is used.
– What is redundancy ? What are the problems associated with redundancy?
– What is data redundancy and which characteristics of the file systems can
lead to it.
• List all the database users. Explain sophisticated users and specialized users.
– Who are sophisticated users? Describe them.
• What is data dictionary?

Entity-Relationship(E-R)
Modeling

ER model
ER Model Stands for Entity Relationship Model
• The Entity-Relationship (ER) model was originally
proposed by Peter in 1976.
• The ER model is a conceptual data model that views
the real world as entities and relationships.
• A graphical technique for understanding and
organizing the data independent of the actual
database implementation
• The basic object that the ER model represents is an
entity.

Definition Entity
Entity - A ‘thing’ or an ‘object’ that is
distinguishable from all the other objects.
Each entity has a set of properties. For
example, each person in an enterprise is an
entity with properties person-id, name, age
etc.

Definition Entity
Entity - is a thing in the real world with an
independent existence and about which we
intend to collect data.
An entity may be an object with a physical
existence (ex a particular person, car, house,
or employee)
It may be an object with a conceptual existence
( a company, a job, or a university course)

Definition Entity Set
Entity Set - Set of entities of the same type that
share the same properties or attributes. For
example, employees of a store. Each
employee of the store share the common
properties such as empid, name, date of
joining, salary etc. This is also known as
Entity type.
Entity instance: a particular member of the
entity type e.g. a particular student

Attributes - Properties/characteristics that
describe entities.
Ex – An EMPLOYEEE entity may be described by
the employee’s name, age, address, salary
and job.
Attributes maybe single or multi-valued, simple
or composite, stored or derived.
Definition Attributes

Relationship – Is an association between
several entities. For example, a car is owned
by a person.
Relationships can be recursive. For example, a
student helps a student. Both belong to the
same entity set of students.
Definition Relationship

Definition of Attribute
Attribute – Attributes are the properties of an
Entity.
For ex- If STUSENT is an Entity set, then Roll,
Name, Gender, Age, Sem are the attributes of
a student.

Represented by ellipses connected to the entity type by straight
lines

Represented by an ellipse from which other ellipses emanate and represent the
component attributes. E.g Address.

Indicated by a double lined ellipse as shown in the figure.

NOTE – DOJ – DATE OF JOINING
YOS – YEAR OF SERVICE
EMPLOYEE
EID ENAME DOJ YOS

Note – Regular Entity is also called Strong Entity
Weak Entity is represented by double rectangle
spouse

E.G If Works-for is the relationship between the Employee entity and
the department entity, then Ram works for Comp.sc department,
shyam works –for electrical department ..etc are relationship instances
of the relationship, works-for

Relationship is represented by a diamond
symbol.
EMPLOYEE DEPT
WORKS
FOR
The relationship above is read as EMPLOYEE WORKS-FOR
DEPARTMENT

A relationship is represented as a diamond between two entity types.
It has a label that explains the relationship. Usually the convention is
to read the ER diagram from top to bottom and from left to right.
So, the relationship name is so chosen as to make sense when read
from left to right.
The relationship above is read as student enrolls-in course

A unary relationship is represented as a diamond which connects
one entity to itself as a loop.
The relationship above means, some instances of Employee
manage other instances of Employee.

A relationship between two entity types.

A relationship connecting three entity types.

Constraints on Relationship Type
Relationship type usually have certain constraints
that limit the possible combinations of entities
that may participate in the corresponding
relationship set.
For ex – if the company has a rule that each
employee must work for exactly one
department, then we would like to describe this
constraint in the schema.
Two main types of relationship constraint –
– Cardinality
– Participation

The minimum and maximum values of this connectivity is called the cardinality of the
relationship
Cardinality – Specifies how many instances of an entity relate to
one instance of another entity

EMPLOYEE DEPT
WORKS
FOR
1 1
1 TO 1

1 TO 1
PERSON CHAIR
SITS ON
1 1

1 TO MANY
ORGANIZATION EMPLOYEE
HAS
1 N

MANY TO 1
EMPLOYEE DEPT
WORKS
FOR
N 1

MANY TO MANY
STUDENT COURSE
ENROLLS
FOR
N N

Participation Constraint
Participation constraint specifies whether the existence of
an entity depends on its being related to another entity
via the relationship type. This specifies the minimum
number of relationship instances that each entity can
participate in.
This is of two types
Total
partial
Ex- If a company policy states that “every employee must
work for a department” then an employee entity
exists only if it participates in at least one WORK-FOR
relationship instance. Thus the participation of
EMPLOYEE in WORKS-FOR is called total participation.

All employees will not be head-of some department. So only few instances of
employee entity participate in the above relationship. But each department will be
headed by some employee. So department entity’s participation is total and
employee entity’s participation is partial in the above relationship.

•All instances of the entity type Employee don’t participate in the relationship, Head-of.
•Every employee doesn’t head a department. So, employee entity type is said to partially
participate in the relationship.
•But, every department would be headed by some employee.
•So, all instances of the entity type Department participate in this relationship. So, we say that
it is total participation from the department side.

EMPLOYEE WORKS
FOR
DEPARTMENT
Total
participation

These attributes best describe the relationship rather
than any individual entity.

The identifying relationship is the one which relates the
weak entity with the strong entity on which it depends.

Class Hierarchies
(Specialization and Generalization)
• Class hierarchies can be viewed in one of two ways:
People
--Students
Graduate
Undergraduate
Part time
Full time
--Employees
Academic
Non-academic
Permanent
Contract

Class Hierarchies
(Specialization and Generalization)
Specialization –
• It is a top-down approach.
• Specialization is the process of identifying the
subsets of a superclass (entity set) that share
some special attributes.
• In our example People entity can be
specialized into Students entity and
Employees.

Specialization –
PEOPLE
STUDENTS EMPLOYEES
IS
A

Generalization-
• It is a Bottom Up Approach
• Generalization is the process of identifying
common characteristics from a collection of
entity sets and creating a new set that
possesses these characteristics.
• In our example Students and Employees can
be generalized into People.

Aggregation
• So far we have seen that, a relationship set is
an association between entity sets.
• Sometimes we have to model a relationship
between a collection of entities and
relationships.
• For this we use the concept of Aggregation

Example of Aggregation
Suppose we have an entity set called Projects and
that each Projects entity is sponsored by one or
more departments. The Sponsors relationship set
captures this information. A department that
sponsors a project might assign employees to
monitor the sponsorship. Intuitively, Monitors
should be a relationship set that associates a
Sponsors relationship with an Employee entity.
For this we need Aggregation. This can be
illustrated with a dashed box around sponsors
used to denote aggregation

EMPLOYEE
EID NAME DID
MONITORS
PROJECTS
PID
START
_DT DID
DEPARTMENTS
EID NAME DID
SPONSORS
SINCE
DID

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