Data Models

DATA MODELS INTRODUCTION
• A Data Model is a set of concepts that can be used
to describe the structure of data in a database.
• A database model shows the logical structure of a
database, including the relationships and constraints
that determine how data can be stored and
accessed.
• Data Models are used to support the development of
information systems by providing the definition and
format of data to be involved in future systems.
• Data model also gives idea about possible alternatives
to achieve targeted solution.
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Types of Data Models
• Hierarchical Model
• Network Model
• Relational Model
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Hierarchical Model
• This model is developed by IBM and
North American Rockwell Known as
Information Management System.
• This is the oldest and simplest DBMS
model.
• The model is sorted hierarchical ,either in
top down or bottom up approach of
designing.
• This model uses pointers to navigate
between stored data.
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Example of Hierarchical Model
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Business Rule
• One parent node can have many child
nodes ,but one child cannot have
more than one parent.
• Relationship is one to many.
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Advantages of Hierarchical Model
1. Conceptual simplicity
• Relationship between various level
is logically very simple. Hence
database structure becomes
easier to view.
2. Database Security
• Security is given by DBMS system
itself.
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3. Simple creation ,Updation and Access
• This model is simple to construct
with help of pointers .
• Easy to understand .
• Easy to delete and add records in the
database using pointers .
• This is faster and easy data retrival
through higher level records in tree
structure.
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4. Database Integrity
• There is parent child association
between different levels of
records in files.
• Child record is attached with the
parent record which maintains the
integrity
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5. Efficiency
• This model having good
performance when database
contains large amount of data in
which one record has many
related records like a class
contains many students studying
in it.
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Disadvantages of Hierarchical Model
1. Complex Implementation
• Programmers and designers need to
have knowledge of physical data storage
which may be complex.
2. Difficult to manage
• Any change in a location of data needs
change in all application programs that
accesses changes data.
• Data access is restricted by pointer path.
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3. Limitations in implementation
• It is difficult to implement many to
many relationship.
• Query optimization is not possible
or possible up to certain extent.
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Network Model
• This model is similar to Hierarchical
model, this model also uses pointers
toward data but there is no need of
parent to child association .
• It uses graph data structure.
• A child can have more than one parent.
• It has one to many or many to many
relationship.
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• A relationship between any two record
types is called as a set.
• Data in network model are
represented by collection of records
and relationships among data are
represented by links, which can be
viewed as pointers.
• The records in the database are
organized as collection of arbitrary
groups.
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Example of Network Model
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Advantages of Network Model
1. Simple design
• The network model is simple and
easy to design and understand.
2. Ability to handle many types of
relationship
• The network model can handle the
one to many or many to many or
other relationships.
• Hence network model manages
multiuser environment.
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3. Ease of data access
• In a network model, an application can
access a root(parent) record and all the
member records within a SET (child).
• Provide very efficient and high speed
retrieval.
4. Data Integrity
• In a network model, no member can exist
without a parent entity.
• A user must first define the root record and
then the child record.
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5. Data Independence
• In network model, application
programs work independently of the
data.
• Any changes made in the data do not
affect the application programs.
• In a network model ,administrators
offer data creation by DDL and DML.
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Disadvantages of Network Model
1. System Complexity
• In a network model ,data are accessed
one record at a time.
• This can increase the complexity of
system for accessing multiple records at
a time.
2. Lack of structural independence
• Any changes made to the database
structure require the application
programs to be modified before it can
access data.
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Relational Model
• The Relational Model is first proposed by E.F
Codd.
• This model uses collection of tables to represent
relationships amongst the data.
• In this model ,each database item is viewed as a
record with attributes. A set of records with
similar attributes is called a TABLE. Each table
contains a record of a particular type.
• The database uses Relational model called as
RDBMS .
• A Relational database is a collection of 2-D tables
which consist of rows and columns.
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• Relational model is the most popular model and the
most extensively used model.
• In this model the data can be stored in the “tables”
and this storing is called as “relation”, the relations
can be normalized and the normalized relation values
are called atomic values.
• Each row in a relation contains unique value and it is
called as “tuple”, each column contains value from
same domain and it is called as “attribute”.
• Most of the popular commercial DBMS products like
Oracle, Sybase , MySQL, are based on relational
model.
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• A particular attribute or combination of
attributes is chosen as a primary key that can be
referred to in other tables, when it’s called a
foreign key.
• The model also accounts for the types of
relationships between those tables, including
one-to-one, one-to-many, and many-to-many
relationships.
• Within the database, tables can be normalized
that make the database flexible, adaptable, and
scalable. When normalized, each piece of data is
atomic, or broken into the smallest useful pieces.
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Example of Relational Model
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ADVANTAGES OF RELATIONAL MODEL
1. Relational Algebra
• A relational database supports
relational algebra and also relational
operations of the set theory like
union , intersection ,difference ,
cartisen product , relational database
also support select , project , join
and division operations.
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2. Dynamic Views
• In a RDBMS , a view is not a part of
the physical schema , it is always
dynamic.
3. Structured query language (SQL)
• For data access in RDBMS we have
query language SQL .Most of the
database vendors support the SQL
standards.
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4. Excellent data security
• Relational databases support the
concept of user rights, every user is
assigned with some database
permission called as user rights.
• Relational databases are scalable and
provide good support for the
implementation of distributed systems
and other advanced database
systems.
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Data Models

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